From 61598093bbdd283a7edc367d900f223070ead8d2 Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Fri, 10 May 2024 07:43:03 +0000
Subject: [PATCH] add ax88772C AX88772C_eeprom_tools
---
kernel/kernel/rcu/tree_plugin.h | 2536 ++++++++++++++++++++++++++++------------------------------
1 files changed, 1,227 insertions(+), 1,309 deletions(-)
diff --git a/kernel/kernel/rcu/tree_plugin.h b/kernel/kernel/rcu/tree_plugin.h
index 5f6de49..f5ba074 100644
--- a/kernel/kernel/rcu/tree_plugin.h
+++ b/kernel/kernel/rcu/tree_plugin.h
@@ -1,63 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
* Internal non-public definitions that provide either classic
* or preemptible semantics.
*
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
* Copyright Red Hat, 2009
* Copyright IBM Corporation, 2009
*
* Author: Ingo Molnar <mingo@elte.hu>
- * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ * Paul E. McKenney <paulmck@linux.ibm.com>
*/
-
-#include <linux/delay.h>
-#include <linux/gfp.h>
-#include <linux/oom.h>
-#include <linux/sched/debug.h>
-#include <linux/smpboot.h>
-#include <linux/sched/isolation.h>
-#include <uapi/linux/sched/types.h>
-#include "../time/tick-internal.h"
-
-#ifdef CONFIG_RCU_BOOST
#include "../locking/rtmutex_common.h"
-
-/*
- * Control variables for per-CPU and per-rcu_node kthreads. These
- * handle all flavors of RCU.
- */
-static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
-DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
-DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
-DEFINE_PER_CPU(char, rcu_cpu_has_work);
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
- * all uses are in dead code. Provide a definition to keep the compiler
- * happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
- * This probably needs to be excluded from -rt builds.
- */
-#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
-#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
-
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifdef CONFIG_RCU_NOCB_CPU
static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
@@ -82,6 +36,8 @@
pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
if (IS_ENABLED(CONFIG_PROVE_RCU))
pr_info("\tRCU lockdep checking is enabled.\n");
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ pr_info("\tRCU strict (and thus non-scalable) grace periods enabled.\n");
if (RCU_NUM_LVLS >= 4)
pr_info("\tFour(or more)-level hierarchy is enabled.\n");
if (RCU_FANOUT_LEAF != 16)
@@ -102,10 +58,14 @@
pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
if (qlowmark != DEFAULT_RCU_QLOMARK)
pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
+ if (qovld != DEFAULT_RCU_QOVLD)
+ pr_info("\tBoot-time adjustment of callback overload level to %ld.\n", qovld);
if (jiffies_till_first_fqs != ULONG_MAX)
pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
if (jiffies_till_next_fqs != ULONG_MAX)
pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
+ if (jiffies_till_sched_qs != ULONG_MAX)
+ pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
if (rcu_kick_kthreads)
pr_info("\tKick kthreads if too-long grace period.\n");
if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
@@ -116,6 +76,8 @@
pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
if (gp_cleanup_delay)
pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
+ if (!use_softirq)
+ pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
pr_info("\tRCU debug extended QS entry/exit.\n");
rcupdate_announce_bootup_oddness();
@@ -123,12 +85,7 @@
#ifdef CONFIG_PREEMPT_RCU
-RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
-static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
-static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
-
-static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
- bool wake);
+static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
static void rcu_read_unlock_special(struct task_struct *t);
/*
@@ -271,7 +228,7 @@
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
}
if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
- rnp->exp_tasks = &t->rcu_node_entry;
+ WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry);
WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
!(rnp->qsmask & rdp->grpmask));
WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
@@ -284,13 +241,10 @@
* no need to check for a subsequent expedited GP. (Though we are
* still in a quiescent state in any case.)
*/
- if (blkd_state & RCU_EXP_BLKD &&
- t->rcu_read_unlock_special.b.exp_need_qs) {
- t->rcu_read_unlock_special.b.exp_need_qs = false;
- rcu_report_exp_rdp(rdp->rsp, rdp, true);
- } else {
- WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
- }
+ if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs)
+ rcu_report_exp_rdp(rdp);
+ else
+ WARN_ON_ONCE(rdp->exp_deferred_qs);
}
/*
@@ -306,16 +260,16 @@
*
* Callers to this function must disable preemption.
*/
-static void rcu_preempt_qs(void)
+static void rcu_qs(void)
{
- RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
- if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
+ RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
+ if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
trace_rcu_grace_period(TPS("rcu_preempt"),
- __this_cpu_read(rcu_data_p->gp_seq),
+ __this_cpu_read(rcu_data.gp_seq),
TPS("cpuqs"));
- __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
- barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
- current->rcu_read_unlock_special.b.need_qs = false;
+ __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
+ barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
+ WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
}
}
@@ -332,19 +286,19 @@
*
* Caller must disable interrupts.
*/
-static void rcu_preempt_note_context_switch(bool preempt)
+void rcu_note_context_switch(bool preempt)
{
struct task_struct *t = current;
- struct rcu_data *rdp;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp;
+ trace_rcu_utilization(TPS("Start context switch"));
lockdep_assert_irqs_disabled();
- WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
- if (t->rcu_read_lock_nesting > 0 &&
+ WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0);
+ if (rcu_preempt_depth() > 0 &&
!t->rcu_read_unlock_special.b.blocked) {
/* Possibly blocking in an RCU read-side critical section. */
- rdp = this_cpu_ptr(rcu_state_p->rda);
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp);
t->rcu_read_unlock_special.b.blocked = true;
@@ -357,20 +311,14 @@
*/
WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
- trace_rcu_preempt_task(rdp->rsp->name,
+ trace_rcu_preempt_task(rcu_state.name,
t->pid,
(rnp->qsmask & rdp->grpmask)
? rnp->gp_seq
: rcu_seq_snap(&rnp->gp_seq));
rcu_preempt_ctxt_queue(rnp, rdp);
- } else if (t->rcu_read_lock_nesting < 0 &&
- t->rcu_read_unlock_special.s) {
-
- /*
- * Complete exit from RCU read-side critical section on
- * behalf of preempted instance of __rcu_read_unlock().
- */
- rcu_read_unlock_special(t);
+ } else {
+ rcu_preempt_deferred_qs(t);
}
/*
@@ -382,8 +330,13 @@
* grace period, then the fact that the task has been enqueued
* means that we continue to block the current grace period.
*/
- rcu_preempt_qs();
+ rcu_qs();
+ if (rdp->exp_deferred_qs)
+ rcu_report_exp_rdp(rdp);
+ rcu_tasks_qs(current, preempt);
+ trace_rcu_utilization(TPS("End context switch"));
}
+EXPORT_SYMBOL_GPL(rcu_note_context_switch);
/*
* Check for preempted RCU readers blocking the current grace period
@@ -395,6 +348,24 @@
return READ_ONCE(rnp->gp_tasks) != NULL;
}
+/* limit value for ->rcu_read_lock_nesting. */
+#define RCU_NEST_PMAX (INT_MAX / 2)
+
+static void rcu_preempt_read_enter(void)
+{
+ current->rcu_read_lock_nesting++;
+}
+
+static int rcu_preempt_read_exit(void)
+{
+ return --current->rcu_read_lock_nesting;
+}
+
+static void rcu_preempt_depth_set(int val)
+{
+ current->rcu_read_lock_nesting = val;
+}
+
/*
* Preemptible RCU implementation for rcu_read_lock().
* Just increment ->rcu_read_lock_nesting, shared state will be updated
@@ -402,7 +373,11 @@
*/
void __rcu_read_lock(void)
{
- current->rcu_read_lock_nesting++;
+ rcu_preempt_read_enter();
+ if (IS_ENABLED(CONFIG_PROVE_LOCKING))
+ WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread)
+ WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true);
barrier(); /* critical section after entry code. */
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
@@ -418,24 +393,16 @@
{
struct task_struct *t = current;
- if (t->rcu_read_lock_nesting != 1) {
- --t->rcu_read_lock_nesting;
- } else {
+ if (rcu_preempt_read_exit() == 0) {
barrier(); /* critical section before exit code. */
- t->rcu_read_lock_nesting = INT_MIN;
- barrier(); /* assign before ->rcu_read_unlock_special load */
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
rcu_read_unlock_special(t);
- barrier(); /* ->rcu_read_unlock_special load before assign */
- t->rcu_read_lock_nesting = 0;
}
-#ifdef CONFIG_PROVE_LOCKING
- {
- int rrln = READ_ONCE(t->rcu_read_lock_nesting);
+ if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
+ int rrln = rcu_preempt_depth();
- WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+ WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX);
}
-#endif /* #ifdef CONFIG_PROVE_LOCKING */
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
@@ -464,27 +431,21 @@
}
/*
- * Handle special cases during rcu_read_unlock(), such as needing to
- * notify RCU core processing or task having blocked during the RCU
- * read-side critical section.
+ * Report deferred quiescent states. The deferral time can
+ * be quite short, for example, in the case of the call from
+ * rcu_read_unlock_special().
*/
-static void rcu_read_unlock_special(struct task_struct *t)
+static void
+rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
{
bool empty_exp;
bool empty_norm;
bool empty_exp_now;
- unsigned long flags;
struct list_head *np;
bool drop_boost_mutex = false;
struct rcu_data *rdp;
struct rcu_node *rnp;
union rcu_special special;
-
- /* NMI handlers cannot block and cannot safely manipulate state. */
- if (in_nmi())
- return;
-
- local_irq_save(flags);
/*
* If RCU core is waiting for this CPU to exit its critical section,
@@ -492,49 +453,32 @@
* t->rcu_read_unlock_special cannot change.
*/
special = t->rcu_read_unlock_special;
+ rdp = this_cpu_ptr(&rcu_data);
+ if (!special.s && !rdp->exp_deferred_qs) {
+ local_irq_restore(flags);
+ return;
+ }
+ t->rcu_read_unlock_special.s = 0;
if (special.b.need_qs) {
- rcu_preempt_qs();
- t->rcu_read_unlock_special.b.need_qs = false;
- if (!t->rcu_read_unlock_special.s) {
- local_irq_restore(flags);
- return;
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
+ rcu_report_qs_rdp(rdp);
+ udelay(rcu_unlock_delay);
+ } else {
+ rcu_qs();
}
}
/*
- * Respond to a request for an expedited grace period, but only if
- * we were not preempted, meaning that we were running on the same
- * CPU throughout. If we were preempted, the exp_need_qs flag
- * would have been cleared at the time of the first preemption,
- * and the quiescent state would be reported when we were dequeued.
+ * Respond to a request by an expedited grace period for a
+ * quiescent state from this CPU. Note that requests from
+ * tasks are handled when removing the task from the
+ * blocked-tasks list below.
*/
- if (special.b.exp_need_qs) {
- WARN_ON_ONCE(special.b.blocked);
- t->rcu_read_unlock_special.b.exp_need_qs = false;
- rdp = this_cpu_ptr(rcu_state_p->rda);
- rcu_report_exp_rdp(rcu_state_p, rdp, true);
- if (!t->rcu_read_unlock_special.s) {
- local_irq_restore(flags);
- return;
- }
- }
-
- /* Hardware IRQ handlers cannot block, complain if they get here. */
- if (in_irq() || in_serving_softirq()) {
- lockdep_rcu_suspicious(__FILE__, __LINE__,
- "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
- pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
- t->rcu_read_unlock_special.s,
- t->rcu_read_unlock_special.b.blocked,
- t->rcu_read_unlock_special.b.exp_need_qs,
- t->rcu_read_unlock_special.b.need_qs);
- local_irq_restore(flags);
- return;
- }
+ if (rdp->exp_deferred_qs)
+ rcu_report_exp_rdp(rdp);
/* Clean up if blocked during RCU read-side critical section. */
if (special.b.blocked) {
- t->rcu_read_unlock_special.b.blocked = false;
/*
* Remove this task from the list it blocked on. The task
@@ -549,7 +493,7 @@
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
(!empty_norm || rnp->qsmask));
- empty_exp = sync_rcu_preempt_exp_done(rnp);
+ empty_exp = sync_rcu_exp_done(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
np = rcu_next_node_entry(t, rnp);
list_del_init(&t->rcu_node_entry);
@@ -559,12 +503,12 @@
if (&t->rcu_node_entry == rnp->gp_tasks)
WRITE_ONCE(rnp->gp_tasks, np);
if (&t->rcu_node_entry == rnp->exp_tasks)
- rnp->exp_tasks = np;
+ WRITE_ONCE(rnp->exp_tasks, np);
if (IS_ENABLED(CONFIG_RCU_BOOST)) {
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
if (&t->rcu_node_entry == rnp->boost_tasks)
- rnp->boost_tasks = np;
+ WRITE_ONCE(rnp->boost_tasks, np);
}
/*
@@ -573,7 +517,7 @@
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
* so we must take a snapshot of the expedited state.
*/
- empty_exp_now = sync_rcu_preempt_exp_done(rnp);
+ empty_exp_now = sync_rcu_exp_done(rnp);
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
rnp->gp_seq,
@@ -582,138 +526,141 @@
rnp->grplo,
rnp->grphi,
!!rnp->gp_tasks);
- rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
+ rcu_report_unblock_qs_rnp(rnp, flags);
} else {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
-
- /* Unboost if we were boosted. */
- if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
- rt_mutex_futex_unlock(&rnp->boost_mtx);
/*
* If this was the last task on the expedited lists,
* then we need to report up the rcu_node hierarchy.
*/
if (!empty_exp && empty_exp_now)
- rcu_report_exp_rnp(rcu_state_p, rnp, true);
+ rcu_report_exp_rnp(rnp, true);
+
+ /* Unboost if we were boosted. */
+ if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
+ rt_mutex_futex_unlock(&rnp->boost_mtx);
+
} else {
local_irq_restore(flags);
}
}
/*
- * Dump detailed information for all tasks blocking the current RCU
- * grace period on the specified rcu_node structure.
+ * Is a deferred quiescent-state pending, and are we also not in
+ * an RCU read-side critical section? It is the caller's responsibility
+ * to ensure it is otherwise safe to report any deferred quiescent
+ * states. The reason for this is that it is safe to report a
+ * quiescent state during context switch even though preemption
+ * is disabled. This function cannot be expected to understand these
+ * nuances, so the caller must handle them.
*/
-static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
+{
+ return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
+ READ_ONCE(t->rcu_read_unlock_special.s)) &&
+ rcu_preempt_depth() == 0;
+}
+
+/*
+ * Report a deferred quiescent state if needed and safe to do so.
+ * As with rcu_preempt_need_deferred_qs(), "safe" involves only
+ * not being in an RCU read-side critical section. The caller must
+ * evaluate safety in terms of interrupt, softirq, and preemption
+ * disabling.
+ */
+static void rcu_preempt_deferred_qs(struct task_struct *t)
{
unsigned long flags;
- struct task_struct *t;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- if (!rcu_preempt_blocked_readers_cgp(rnp)) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ if (!rcu_preempt_need_deferred_qs(t))
+ return;
+ local_irq_save(flags);
+ rcu_preempt_deferred_qs_irqrestore(t, flags);
+}
+
+/*
+ * Minimal handler to give the scheduler a chance to re-evaluate.
+ */
+static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
+{
+ struct rcu_data *rdp;
+
+ rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
+ rdp->defer_qs_iw_pending = false;
+}
+
+/*
+ * Handle special cases during rcu_read_unlock(), such as needing to
+ * notify RCU core processing or task having blocked during the RCU
+ * read-side critical section.
+ */
+static void rcu_read_unlock_special(struct task_struct *t)
+{
+ unsigned long flags;
+ bool preempt_bh_were_disabled =
+ !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
+ bool irqs_were_disabled;
+
+ /* NMI handlers cannot block and cannot safely manipulate state. */
+ if (in_nmi())
+ return;
+
+ local_irq_save(flags);
+ irqs_were_disabled = irqs_disabled_flags(flags);
+ if (preempt_bh_were_disabled || irqs_were_disabled) {
+ bool exp;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+ struct rcu_node *rnp = rdp->mynode;
+
+ exp = (t->rcu_blocked_node &&
+ READ_ONCE(t->rcu_blocked_node->exp_tasks)) ||
+ (rdp->grpmask & READ_ONCE(rnp->expmask));
+ // Need to defer quiescent state until everything is enabled.
+ if (use_softirq && (in_irq() || (exp && !irqs_were_disabled))) {
+ // Using softirq, safe to awaken, and either the
+ // wakeup is free or there is an expedited GP.
+ raise_softirq_irqoff(RCU_SOFTIRQ);
+ } else {
+ // Enabling BH or preempt does reschedule, so...
+ // Also if no expediting, slow is OK.
+ // Plus nohz_full CPUs eventually get tick enabled.
+ set_tsk_need_resched(current);
+ set_preempt_need_resched();
+ if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
+ !rdp->defer_qs_iw_pending && exp && cpu_online(rdp->cpu)) {
+ // Get scheduler to re-evaluate and call hooks.
+ // If !IRQ_WORK, FQS scan will eventually IPI.
+ init_irq_work(&rdp->defer_qs_iw,
+ rcu_preempt_deferred_qs_handler);
+ rdp->defer_qs_iw_pending = true;
+ irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
+ }
+ }
+ local_irq_restore(flags);
return;
}
- t = list_entry(rnp->gp_tasks->prev,
- struct task_struct, rcu_node_entry);
- list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- /*
- * We could be printing a lot while holding a spinlock.
- * Avoid triggering hard lockup.
- */
- touch_nmi_watchdog();
- sched_show_task(t);
- }
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-}
-
-/*
- * Dump detailed information for all tasks blocking the current RCU
- * grace period.
- */
-static void rcu_print_detail_task_stall(struct rcu_state *rsp)
-{
- struct rcu_node *rnp = rcu_get_root(rsp);
-
- rcu_print_detail_task_stall_rnp(rnp);
- rcu_for_each_leaf_node(rsp, rnp)
- rcu_print_detail_task_stall_rnp(rnp);
-}
-
-static void rcu_print_task_stall_begin(struct rcu_node *rnp)
-{
- pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
- rnp->level, rnp->grplo, rnp->grphi);
-}
-
-static void rcu_print_task_stall_end(void)
-{
- pr_cont("\n");
-}
-
-/*
- * Scan the current list of tasks blocked within RCU read-side critical
- * sections, printing out the tid of each.
- */
-static int rcu_print_task_stall(struct rcu_node *rnp)
-{
- struct task_struct *t;
- int ndetected = 0;
-
- if (!rcu_preempt_blocked_readers_cgp(rnp))
- return 0;
- rcu_print_task_stall_begin(rnp);
- t = list_entry(rnp->gp_tasks->prev,
- struct task_struct, rcu_node_entry);
- list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- pr_cont(" P%d", t->pid);
- ndetected++;
- }
- rcu_print_task_stall_end();
- return ndetected;
-}
-
-/*
- * Scan the current list of tasks blocked within RCU read-side critical
- * sections, printing out the tid of each that is blocking the current
- * expedited grace period.
- */
-static int rcu_print_task_exp_stall(struct rcu_node *rnp)
-{
- struct task_struct *t;
- int ndetected = 0;
-
- if (!rnp->exp_tasks)
- return 0;
- t = list_entry(rnp->exp_tasks->prev,
- struct task_struct, rcu_node_entry);
- list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- pr_cont(" P%d", t->pid);
- ndetected++;
- }
- return ndetected;
+ rcu_preempt_deferred_qs_irqrestore(t, flags);
}
/*
* Check that the list of blocked tasks for the newly completed grace
* period is in fact empty. It is a serious bug to complete a grace
* period that still has RCU readers blocked! This function must be
- * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock
- * must be held by the caller.
+ * invoked -before- updating this rnp's ->gp_seq.
*
* Also, if there are blocked tasks on the list, they automatically
* block the newly created grace period, so set up ->gp_tasks accordingly.
*/
-static void
-rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
struct task_struct *t;
RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
+ raw_lockdep_assert_held_rcu_node(rnp);
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
- dump_blkd_tasks(rsp, rnp, 10);
+ dump_blkd_tasks(rnp, 10);
if (rcu_preempt_has_tasks(rnp) &&
(rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
@@ -726,139 +673,67 @@
}
/*
- * Check for a quiescent state from the current CPU. When a task blocks,
- * the task is recorded in the corresponding CPU's rcu_node structure,
- * which is checked elsewhere.
- *
- * Caller must disable hard irqs.
+ * Check for a quiescent state from the current CPU, including voluntary
+ * context switches for Tasks RCU. When a task blocks, the task is
+ * recorded in the corresponding CPU's rcu_node structure, which is checked
+ * elsewhere, hence this function need only check for quiescent states
+ * related to the current CPU, not to those related to tasks.
*/
-static void rcu_preempt_check_callbacks(void)
+static void rcu_flavor_sched_clock_irq(int user)
{
- struct rcu_state *rsp = &rcu_preempt_state;
struct task_struct *t = current;
- if (t->rcu_read_lock_nesting == 0) {
- rcu_preempt_qs();
+ lockdep_assert_irqs_disabled();
+ if (user || rcu_is_cpu_rrupt_from_idle()) {
+ rcu_note_voluntary_context_switch(current);
+ }
+ if (rcu_preempt_depth() > 0 ||
+ (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
+ /* No QS, force context switch if deferred. */
+ if (rcu_preempt_need_deferred_qs(t)) {
+ set_tsk_need_resched(t);
+ set_preempt_need_resched();
+ }
+ } else if (rcu_preempt_need_deferred_qs(t)) {
+ rcu_preempt_deferred_qs(t); /* Report deferred QS. */
+ return;
+ } else if (!WARN_ON_ONCE(rcu_preempt_depth())) {
+ rcu_qs(); /* Report immediate QS. */
return;
}
- if (t->rcu_read_lock_nesting > 0 &&
- __this_cpu_read(rcu_data_p->core_needs_qs) &&
- __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm) &&
+
+ /* If GP is oldish, ask for help from rcu_read_unlock_special(). */
+ if (rcu_preempt_depth() > 0 &&
+ __this_cpu_read(rcu_data.core_needs_qs) &&
+ __this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
!t->rcu_read_unlock_special.b.need_qs &&
- time_after(jiffies, rsp->gp_start + HZ))
+ time_after(jiffies, rcu_state.gp_start + HZ))
t->rcu_read_unlock_special.b.need_qs = true;
-}
-
-/**
- * call_rcu() - Queue an RCU callback for invocation after a grace period.
- * @head: structure to be used for queueing the RCU updates.
- * @func: actual callback function to be invoked after the grace period
- *
- * The callback function will be invoked some time after a full grace
- * period elapses, in other words after all pre-existing RCU read-side
- * critical sections have completed. However, the callback function
- * might well execute concurrently with RCU read-side critical sections
- * that started after call_rcu() was invoked. RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
- *
- * Note that all CPUs must agree that the grace period extended beyond
- * all pre-existing RCU read-side critical section. On systems with more
- * than one CPU, this means that when "func()" is invoked, each CPU is
- * guaranteed to have executed a full memory barrier since the end of its
- * last RCU read-side critical section whose beginning preceded the call
- * to call_rcu(). It also means that each CPU executing an RCU read-side
- * critical section that continues beyond the start of "func()" must have
- * executed a memory barrier after the call_rcu() but before the beginning
- * of that RCU read-side critical section. Note that these guarantees
- * include CPUs that are offline, idle, or executing in user mode, as
- * well as CPUs that are executing in the kernel.
- *
- * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
- * resulting RCU callback function "func()", then both CPU A and CPU B are
- * guaranteed to execute a full memory barrier during the time interval
- * between the call to call_rcu() and the invocation of "func()" -- even
- * if CPU A and CPU B are the same CPU (but again only if the system has
- * more than one CPU).
- */
-void call_rcu(struct rcu_head *head, rcu_callback_t func)
-{
- __call_rcu(head, func, rcu_state_p, -1, 0);
-}
-EXPORT_SYMBOL_GPL(call_rcu);
-
-/**
- * synchronize_rcu - wait until a grace period has elapsed.
- *
- * Control will return to the caller some time after a full grace
- * period has elapsed, in other words after all currently executing RCU
- * read-side critical sections have completed. Note, however, that
- * upon return from synchronize_rcu(), the caller might well be executing
- * concurrently with new RCU read-side critical sections that began while
- * synchronize_rcu() was waiting. RCU read-side critical sections are
- * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
- *
- * See the description of synchronize_sched() for more detailed
- * information on memory-ordering guarantees. However, please note
- * that -only- the memory-ordering guarantees apply. For example,
- * synchronize_rcu() is -not- guaranteed to wait on things like code
- * protected by preempt_disable(), instead, synchronize_rcu() is -only-
- * guaranteed to wait on RCU read-side critical sections, that is, sections
- * of code protected by rcu_read_lock().
- */
-void synchronize_rcu(void)
-{
- RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
- lock_is_held(&rcu_lock_map) ||
- lock_is_held(&rcu_sched_lock_map),
- "Illegal synchronize_rcu() in RCU read-side critical section");
- if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
- return;
- if (rcu_gp_is_expedited())
- synchronize_rcu_expedited();
- else
- wait_rcu_gp(call_rcu);
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu);
-
-/**
- * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
- *
- * Note that this primitive does not necessarily wait for an RCU grace period
- * to complete. For example, if there are no RCU callbacks queued anywhere
- * in the system, then rcu_barrier() is within its rights to return
- * immediately, without waiting for anything, much less an RCU grace period.
- */
-void rcu_barrier(void)
-{
- _rcu_barrier(rcu_state_p);
-}
-EXPORT_SYMBOL_GPL(rcu_barrier);
-
-/*
- * Initialize preemptible RCU's state structures.
- */
-static void __init __rcu_init_preempt(void)
-{
- rcu_init_one(rcu_state_p);
}
/*
* Check for a task exiting while in a preemptible-RCU read-side
- * critical section, clean up if so. No need to issue warnings,
- * as debug_check_no_locks_held() already does this if lockdep
- * is enabled.
+ * critical section, clean up if so. No need to issue warnings, as
+ * debug_check_no_locks_held() already does this if lockdep is enabled.
+ * Besides, if this function does anything other than just immediately
+ * return, there was a bug of some sort. Spewing warnings from this
+ * function is like as not to simply obscure important prior warnings.
*/
void exit_rcu(void)
{
struct task_struct *t = current;
- if (likely(list_empty(¤t->rcu_node_entry)))
+ if (unlikely(!list_empty(¤t->rcu_node_entry))) {
+ rcu_preempt_depth_set(1);
+ barrier();
+ WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
+ } else if (unlikely(rcu_preempt_depth())) {
+ rcu_preempt_depth_set(1);
+ } else {
return;
- t->rcu_read_lock_nesting = 1;
- barrier();
- t->rcu_read_unlock_special.b.blocked = true;
+ }
__rcu_read_unlock();
+ rcu_preempt_deferred_qs(current);
}
/*
@@ -866,7 +741,7 @@
* specified number of elements.
*/
static void
-dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
+dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
{
int cpu;
int i;
@@ -878,23 +753,23 @@
raw_lockdep_assert_held_rcu_node(rnp);
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
__func__, rnp->grplo, rnp->grphi, rnp->level,
- (long)rnp->gp_seq, (long)rnp->completedqs);
+ (long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs);
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
- __func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks,
- rnp->exp_tasks);
+ __func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
+ READ_ONCE(rnp->exp_tasks));
pr_info("%s: ->blkd_tasks", __func__);
i = 0;
list_for_each(lhp, &rnp->blkd_tasks) {
pr_cont(" %p", lhp);
- if (++i >= 10)
+ if (++i >= ncheck)
break;
}
pr_cont("\n");
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
+ rdp = per_cpu_ptr(&rcu_data, cpu);
onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
cpu, ".o"[onl],
@@ -905,7 +780,23 @@
#else /* #ifdef CONFIG_PREEMPT_RCU */
-static struct rcu_state *const rcu_state_p = &rcu_sched_state;
+/*
+ * If strict grace periods are enabled, and if the calling
+ * __rcu_read_unlock() marks the beginning of a quiescent state, immediately
+ * report that quiescent state and, if requested, spin for a bit.
+ */
+void rcu_read_unlock_strict(void)
+{
+ struct rcu_data *rdp;
+
+ if (!IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
+ irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
+ return;
+ rdp = this_cpu_ptr(&rcu_data);
+ rcu_report_qs_rdp(rdp);
+ udelay(rcu_unlock_delay);
+}
+EXPORT_SYMBOL_GPL(rcu_read_unlock_strict);
/*
* Tell them what RCU they are running.
@@ -917,12 +808,73 @@
}
/*
- * Because preemptible RCU does not exist, we never have to check for
- * CPUs being in quiescent states.
+ * Note a quiescent state for PREEMPTION=n. Because we do not need to know
+ * how many quiescent states passed, just if there was at least one since
+ * the start of the grace period, this just sets a flag. The caller must
+ * have disabled preemption.
*/
-static void rcu_preempt_note_context_switch(bool preempt)
+static void rcu_qs(void)
{
+ RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
+ if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
+ return;
+ trace_rcu_grace_period(TPS("rcu_sched"),
+ __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
+ __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
+ if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
+ return;
+ __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
+ rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
}
+
+/*
+ * Register an urgently needed quiescent state. If there is an
+ * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
+ * dyntick-idle quiescent state visible to other CPUs, which will in
+ * some cases serve for expedited as well as normal grace periods.
+ * Either way, register a lightweight quiescent state.
+ */
+void rcu_all_qs(void)
+{
+ unsigned long flags;
+
+ if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
+ return;
+ preempt_disable();
+ /* Load rcu_urgent_qs before other flags. */
+ if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
+ preempt_enable();
+ return;
+ }
+ this_cpu_write(rcu_data.rcu_urgent_qs, false);
+ if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
+ local_irq_save(flags);
+ rcu_momentary_dyntick_idle();
+ local_irq_restore(flags);
+ }
+ rcu_qs();
+ preempt_enable();
+}
+EXPORT_SYMBOL_GPL(rcu_all_qs);
+
+/*
+ * Note a PREEMPTION=n context switch. The caller must have disabled interrupts.
+ */
+void rcu_note_context_switch(bool preempt)
+{
+ trace_rcu_utilization(TPS("Start context switch"));
+ rcu_qs();
+ /* Load rcu_urgent_qs before other flags. */
+ if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
+ goto out;
+ this_cpu_write(rcu_data.rcu_urgent_qs, false);
+ if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
+ rcu_momentary_dyntick_idle();
+ rcu_tasks_qs(current, preempt);
+out:
+ trace_rcu_utilization(TPS("End context switch"));
+}
+EXPORT_SYMBOL_GPL(rcu_note_context_switch);
/*
* Because preemptible RCU does not exist, there are never any preempted
@@ -942,66 +894,47 @@
}
/*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections.
+ * Because there is no preemptible RCU, there can be no deferred quiescent
+ * states.
*/
-static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
{
+ return false;
}
-
-/*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections.
- */
-static int rcu_print_task_stall(struct rcu_node *rnp)
-{
- return 0;
-}
-
-/*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections that are
- * blocking the current expedited grace period.
- */
-static int rcu_print_task_exp_stall(struct rcu_node *rnp)
-{
- return 0;
-}
+static void rcu_preempt_deferred_qs(struct task_struct *t) { }
/*
* Because there is no preemptible RCU, there can be no readers blocked,
* so there is no need to check for blocked tasks. So check only for
* bogus qsmask values.
*/
-static void
-rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
WARN_ON_ONCE(rnp->qsmask);
}
/*
- * Because preemptible RCU does not exist, it never has any callbacks
- * to check.
+ * Check to see if this CPU is in a non-context-switch quiescent state,
+ * namely user mode and idle loop.
*/
-static void rcu_preempt_check_callbacks(void)
+static void rcu_flavor_sched_clock_irq(int user)
{
-}
+ if (user || rcu_is_cpu_rrupt_from_idle()) {
-/*
- * Because preemptible RCU does not exist, rcu_barrier() is just
- * another name for rcu_barrier_sched().
- */
-void rcu_barrier(void)
-{
- rcu_barrier_sched();
-}
-EXPORT_SYMBOL_GPL(rcu_barrier);
+ /*
+ * Get here if this CPU took its interrupt from user
+ * mode or from the idle loop, and if this is not a
+ * nested interrupt. In this case, the CPU is in
+ * a quiescent state, so note it.
+ *
+ * No memory barrier is required here because rcu_qs()
+ * references only CPU-local variables that other CPUs
+ * neither access nor modify, at least not while the
+ * corresponding CPU is online.
+ */
-/*
- * Because preemptible RCU does not exist, it need not be initialized.
- */
-static void __init __rcu_init_preempt(void)
-{
+ rcu_qs();
+ }
}
/*
@@ -1016,24 +949,27 @@
* Dump the guaranteed-empty blocked-tasks state. Trust but verify.
*/
static void
-dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
+dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
{
WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
}
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
-#ifdef CONFIG_RCU_BOOST
-
-static void rcu_wake_cond(struct task_struct *t, int status)
+/*
+ * If boosting, set rcuc kthreads to realtime priority.
+ */
+static void rcu_cpu_kthread_setup(unsigned int cpu)
{
- /*
- * If the thread is yielding, only wake it when this
- * is invoked from idle
- */
- if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
- wake_up_process(t);
+#ifdef CONFIG_RCU_BOOST
+ struct sched_param sp;
+
+ sp.sched_priority = kthread_prio;
+ sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+#endif /* #ifdef CONFIG_RCU_BOOST */
}
+
+#ifdef CONFIG_RCU_BOOST
/*
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
@@ -1113,20 +1049,21 @@
trace_rcu_utilization(TPS("Start boost kthread@init"));
for (;;) {
- rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
+ WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
- rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
+ rcu_wait(READ_ONCE(rnp->boost_tasks) ||
+ READ_ONCE(rnp->exp_tasks));
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
- rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
+ WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
more2boost = rcu_boost(rnp);
if (more2boost)
spincnt++;
else
spincnt = 0;
if (spincnt > 10) {
- rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
+ WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
- schedule_timeout_interruptible(2);
+ schedule_timeout_idle(2);
trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
spincnt = 0;
}
@@ -1149,8 +1086,6 @@
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
__releases(rnp->lock)
{
- struct task_struct *t;
-
raw_lockdep_assert_held_rcu_node(rnp);
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
@@ -1160,33 +1095,15 @@
(rnp->gp_tasks != NULL &&
rnp->boost_tasks == NULL &&
rnp->qsmask == 0 &&
- ULONG_CMP_GE(jiffies, rnp->boost_time))) {
+ (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) {
if (rnp->exp_tasks == NULL)
- rnp->boost_tasks = rnp->gp_tasks;
+ WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- t = rnp->boost_kthread_task;
- if (t)
- rcu_wake_cond(t, rnp->boost_kthread_status);
+ rcu_wake_cond(rnp->boost_kthread_task,
+ READ_ONCE(rnp->boost_kthread_status));
} else {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
-}
-
-/*
- * Wake up the per-CPU kthread to invoke RCU callbacks.
- */
-static void invoke_rcu_callbacks_kthread(void)
-{
- unsigned long flags;
-
- local_irq_save(flags);
- __this_cpu_write(rcu_cpu_has_work, 1);
- if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
- current != __this_cpu_read(rcu_cpu_kthread_task)) {
- rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
- __this_cpu_read(rcu_cpu_kthread_status));
- }
- local_irq_restore(flags);
}
/*
@@ -1195,7 +1112,7 @@
*/
static bool rcu_is_callbacks_kthread(void)
{
- return __this_cpu_read(rcu_cpu_kthread_task) == current;
+ return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
}
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
@@ -1213,95 +1130,35 @@
* already exist. We only create this kthread for preemptible RCU.
* Returns zero if all is well, a negated errno otherwise.
*/
-static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
- struct rcu_node *rnp)
+static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
{
- int rnp_index = rnp - &rsp->node[0];
+ int rnp_index = rnp - rcu_get_root();
unsigned long flags;
struct sched_param sp;
struct task_struct *t;
- if (rcu_state_p != rsp)
- return 0;
+ if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
+ return;
if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
- return 0;
+ return;
- rsp->boost = 1;
+ rcu_state.boost = 1;
+
if (rnp->boost_kthread_task != NULL)
- return 0;
+ return;
+
t = kthread_create(rcu_boost_kthread, (void *)rnp,
"rcub/%d", rnp_index);
- if (IS_ERR(t))
- return PTR_ERR(t);
+ if (WARN_ON_ONCE(IS_ERR(t)))
+ return;
+
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->boost_kthread_task = t;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
- return 0;
-}
-
-static void rcu_kthread_do_work(void)
-{
- rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
- rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
- rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
-}
-
-static void rcu_cpu_kthread_setup(unsigned int cpu)
-{
- struct sched_param sp;
-
- sp.sched_priority = kthread_prio;
- sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
-}
-
-static void rcu_cpu_kthread_park(unsigned int cpu)
-{
- per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
-}
-
-static int rcu_cpu_kthread_should_run(unsigned int cpu)
-{
- return __this_cpu_read(rcu_cpu_has_work);
-}
-
-/*
- * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
- * RCU softirq used in flavors and configurations of RCU that do not
- * support RCU priority boosting.
- */
-static void rcu_cpu_kthread(unsigned int cpu)
-{
- unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
- char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
- int spincnt;
-
- for (spincnt = 0; spincnt < 10; spincnt++) {
- trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
- local_bh_disable();
- *statusp = RCU_KTHREAD_RUNNING;
- this_cpu_inc(rcu_cpu_kthread_loops);
- local_irq_disable();
- work = *workp;
- *workp = 0;
- local_irq_enable();
- if (work)
- rcu_kthread_do_work();
- local_bh_enable();
- if (*workp == 0) {
- trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
- *statusp = RCU_KTHREAD_WAITING;
- return;
- }
- }
- *statusp = RCU_KTHREAD_YIELDING;
- trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
- schedule_timeout_interruptible(2);
- trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
- *statusp = RCU_KTHREAD_WAITING;
}
/*
@@ -1334,38 +1191,25 @@
free_cpumask_var(cm);
}
-static struct smp_hotplug_thread rcu_cpu_thread_spec = {
- .store = &rcu_cpu_kthread_task,
- .thread_should_run = rcu_cpu_kthread_should_run,
- .thread_fn = rcu_cpu_kthread,
- .thread_comm = "rcuc/%u",
- .setup = rcu_cpu_kthread_setup,
- .park = rcu_cpu_kthread_park,
-};
-
/*
* Spawn boost kthreads -- called as soon as the scheduler is running.
*/
static void __init rcu_spawn_boost_kthreads(void)
{
struct rcu_node *rnp;
- int cpu;
- for_each_possible_cpu(cpu)
- per_cpu(rcu_cpu_has_work, cpu) = 0;
- BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
- rcu_for_each_leaf_node(rcu_state_p, rnp)
- (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
+ rcu_for_each_leaf_node(rnp)
+ rcu_spawn_one_boost_kthread(rnp);
}
static void rcu_prepare_kthreads(int cpu)
{
- struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rdp->mynode;
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
if (rcu_scheduler_fully_active)
- (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
+ rcu_spawn_one_boost_kthread(rnp);
}
#else /* #ifdef CONFIG_RCU_BOOST */
@@ -1374,11 +1218,6 @@
__releases(rnp->lock)
{
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-}
-
-static void invoke_rcu_callbacks_kthread(void)
-{
- WARN_ON_ONCE(1);
}
static bool rcu_is_callbacks_kthread(void)
@@ -1407,18 +1246,19 @@
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
- * Check to see if any future RCU-related work will need to be done
- * by the current CPU, even if none need be done immediately, returning
- * 1 if so. This function is part of the RCU implementation; it is -not-
- * an exported member of the RCU API.
+ * Check to see if any future non-offloaded RCU-related work will need
+ * to be done by the current CPU, even if none need be done immediately,
+ * returning 1 if so. This function is part of the RCU implementation;
+ * it is -not- an exported member of the RCU API.
*
- * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
- * any flavor of RCU.
+ * Because we not have RCU_FAST_NO_HZ, just check whether or not this
+ * CPU has RCU callbacks queued.
*/
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
*nextevt = KTIME_MAX;
- return rcu_cpu_has_callbacks(NULL);
+ return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
+ !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
}
/*
@@ -1437,23 +1277,14 @@
{
}
-/*
- * Don't bother keeping a running count of the number of RCU callbacks
- * posted because CONFIG_RCU_FAST_NO_HZ=n.
- */
-static void rcu_idle_count_callbacks_posted(void)
-{
-}
-
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
/*
* This code is invoked when a CPU goes idle, at which point we want
* to have the CPU do everything required for RCU so that it can enter
- * the energy-efficient dyntick-idle mode. This is handled by a
- * state machine implemented by rcu_prepare_for_idle() below.
+ * the energy-efficient dyntick-idle mode.
*
- * The following three proprocessor symbols control this state machine:
+ * The following preprocessor symbol controls this:
*
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
* to sleep in dyntick-idle mode with RCU callbacks pending. This
@@ -1462,81 +1293,67 @@
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
* system. And if you are -that- concerned about energy efficiency,
* just power the system down and be done with it!
- * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
- * permitted to sleep in dyntick-idle mode with only lazy RCU
- * callbacks pending. Setting this too high can OOM your system.
*
- * The values below work well in practice. If future workloads require
+ * The value below works well in practice. If future workloads require
* adjustment, they can be converted into kernel config parameters, though
* making the state machine smarter might be a better option.
*/
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
-#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
module_param(rcu_idle_gp_delay, int, 0644);
-static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
-module_param(rcu_idle_lazy_gp_delay, int, 0644);
/*
- * Try to advance callbacks for all flavors of RCU on the current CPU, but
- * only if it has been awhile since the last time we did so. Afterwards,
- * if there are any callbacks ready for immediate invocation, return true.
+ * Try to advance callbacks on the current CPU, but only if it has been
+ * awhile since the last time we did so. Afterwards, if there are any
+ * callbacks ready for immediate invocation, return true.
*/
static bool __maybe_unused rcu_try_advance_all_cbs(void)
{
bool cbs_ready = false;
- struct rcu_data *rdp;
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp;
- struct rcu_state *rsp;
/* Exit early if we advanced recently. */
- if (jiffies == rdtp->last_advance_all)
+ if (jiffies == rdp->last_advance_all)
return false;
- rdtp->last_advance_all = jiffies;
+ rdp->last_advance_all = jiffies;
- for_each_rcu_flavor(rsp) {
- rdp = this_cpu_ptr(rsp->rda);
- rnp = rdp->mynode;
+ rnp = rdp->mynode;
- /*
- * Don't bother checking unless a grace period has
- * completed since we last checked and there are
- * callbacks not yet ready to invoke.
- */
- if ((rcu_seq_completed_gp(rdp->gp_seq,
- rcu_seq_current(&rnp->gp_seq)) ||
- unlikely(READ_ONCE(rdp->gpwrap))) &&
- rcu_segcblist_pend_cbs(&rdp->cblist))
- note_gp_changes(rsp, rdp);
+ /*
+ * Don't bother checking unless a grace period has
+ * completed since we last checked and there are
+ * callbacks not yet ready to invoke.
+ */
+ if ((rcu_seq_completed_gp(rdp->gp_seq,
+ rcu_seq_current(&rnp->gp_seq)) ||
+ unlikely(READ_ONCE(rdp->gpwrap))) &&
+ rcu_segcblist_pend_cbs(&rdp->cblist))
+ note_gp_changes(rdp);
- if (rcu_segcblist_ready_cbs(&rdp->cblist))
- cbs_ready = true;
- }
+ if (rcu_segcblist_ready_cbs(&rdp->cblist))
+ cbs_ready = true;
return cbs_ready;
}
/*
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
* to invoke. If the CPU has callbacks, try to advance them. Tell the
- * caller to set the timeout based on whether or not there are non-lazy
- * callbacks.
+ * caller about what to set the timeout.
*
* The caller must have disabled interrupts.
*/
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
unsigned long dj;
lockdep_assert_irqs_disabled();
- /* Snapshot to detect later posting of non-lazy callback. */
- rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
-
- /* If no callbacks, RCU doesn't need the CPU. */
- if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
+ /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
+ if (rcu_segcblist_empty(&rdp->cblist) ||
+ rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) {
*nextevt = KTIME_MAX;
return 0;
}
@@ -1547,83 +1364,59 @@
invoke_rcu_core();
return 1;
}
- rdtp->last_accelerate = jiffies;
+ rdp->last_accelerate = jiffies;
- /* Request timer delay depending on laziness, and round. */
- if (!rdtp->all_lazy) {
- dj = round_up(rcu_idle_gp_delay + jiffies,
- rcu_idle_gp_delay) - jiffies;
- } else {
- dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
- }
+ /* Request timer and round. */
+ dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - jiffies;
+
*nextevt = basemono + dj * TICK_NSEC;
return 0;
}
/*
- * Prepare a CPU for idle from an RCU perspective. The first major task
- * is to sense whether nohz mode has been enabled or disabled via sysfs.
- * The second major task is to check to see if a non-lazy callback has
- * arrived at a CPU that previously had only lazy callbacks. The third
- * major task is to accelerate (that is, assign grace-period numbers to)
- * any recently arrived callbacks.
+ * Prepare a CPU for idle from an RCU perspective. The first major task is to
+ * sense whether nohz mode has been enabled or disabled via sysfs. The second
+ * major task is to accelerate (that is, assign grace-period numbers to) any
+ * recently arrived callbacks.
*
* The caller must have disabled interrupts.
*/
static void rcu_prepare_for_idle(void)
{
bool needwake;
- struct rcu_data *rdp;
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp;
- struct rcu_state *rsp;
int tne;
lockdep_assert_irqs_disabled();
- if (rcu_is_nocb_cpu(smp_processor_id()))
+ if (rcu_segcblist_is_offloaded(&rdp->cblist))
return;
/* Handle nohz enablement switches conservatively. */
tne = READ_ONCE(tick_nohz_active);
- if (tne != rdtp->tick_nohz_enabled_snap) {
- if (rcu_cpu_has_callbacks(NULL))
+ if (tne != rdp->tick_nohz_enabled_snap) {
+ if (!rcu_segcblist_empty(&rdp->cblist))
invoke_rcu_core(); /* force nohz to see update. */
- rdtp->tick_nohz_enabled_snap = tne;
+ rdp->tick_nohz_enabled_snap = tne;
return;
}
if (!tne)
return;
/*
- * If a non-lazy callback arrived at a CPU having only lazy
- * callbacks, invoke RCU core for the side-effect of recalculating
- * idle duration on re-entry to idle.
- */
- if (rdtp->all_lazy &&
- rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
- rdtp->all_lazy = false;
- rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
- invoke_rcu_core();
- return;
- }
-
- /*
* If we have not yet accelerated this jiffy, accelerate all
* callbacks on this CPU.
*/
- if (rdtp->last_accelerate == jiffies)
+ if (rdp->last_accelerate == jiffies)
return;
- rdtp->last_accelerate = jiffies;
- for_each_rcu_flavor(rsp) {
- rdp = this_cpu_ptr(rsp->rda);
- if (!rcu_segcblist_pend_cbs(&rdp->cblist))
- continue;
+ rdp->last_accelerate = jiffies;
+ if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
+ needwake = rcu_accelerate_cbs(rnp, rdp);
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
if (needwake)
- rcu_gp_kthread_wake(rsp);
+ rcu_gp_kthread_wake();
}
}
@@ -1634,240 +1427,58 @@
*/
static void rcu_cleanup_after_idle(void)
{
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
lockdep_assert_irqs_disabled();
- if (rcu_is_nocb_cpu(smp_processor_id()))
+ if (rcu_segcblist_is_offloaded(&rdp->cblist))
return;
if (rcu_try_advance_all_cbs())
invoke_rcu_core();
}
-/*
- * Keep a running count of the number of non-lazy callbacks posted
- * on this CPU. This running counter (which is never decremented) allows
- * rcu_prepare_for_idle() to detect when something out of the idle loop
- * posts a callback, even if an equal number of callbacks are invoked.
- * Of course, callbacks should only be posted from within a trace event
- * designed to be called from idle or from within RCU_NONIDLE().
- */
-static void rcu_idle_count_callbacks_posted(void)
-{
- __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
-}
-
-/*
- * Data for flushing lazy RCU callbacks at OOM time.
- */
-static atomic_t oom_callback_count;
-static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
-
-/*
- * RCU OOM callback -- decrement the outstanding count and deliver the
- * wake-up if we are the last one.
- */
-static void rcu_oom_callback(struct rcu_head *rhp)
-{
- if (atomic_dec_and_test(&oom_callback_count))
- wake_up(&oom_callback_wq);
-}
-
-/*
- * Post an rcu_oom_notify callback on the current CPU if it has at
- * least one lazy callback. This will unnecessarily post callbacks
- * to CPUs that already have a non-lazy callback at the end of their
- * callback list, but this is an infrequent operation, so accept some
- * extra overhead to keep things simple.
- */
-static void rcu_oom_notify_cpu(void *unused)
-{
- struct rcu_state *rsp;
- struct rcu_data *rdp;
-
- for_each_rcu_flavor(rsp) {
- rdp = raw_cpu_ptr(rsp->rda);
- if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
- atomic_inc(&oom_callback_count);
- rsp->call(&rdp->oom_head, rcu_oom_callback);
- }
- }
-}
-
-/*
- * If low on memory, ensure that each CPU has a non-lazy callback.
- * This will wake up CPUs that have only lazy callbacks, in turn
- * ensuring that they free up the corresponding memory in a timely manner.
- * Because an uncertain amount of memory will be freed in some uncertain
- * timeframe, we do not claim to have freed anything.
- */
-static int rcu_oom_notify(struct notifier_block *self,
- unsigned long notused, void *nfreed)
-{
- int cpu;
-
- /* Wait for callbacks from earlier instance to complete. */
- wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
- smp_mb(); /* Ensure callback reuse happens after callback invocation. */
-
- /*
- * Prevent premature wakeup: ensure that all increments happen
- * before there is a chance of the counter reaching zero.
- */
- atomic_set(&oom_callback_count, 1);
-
- for_each_online_cpu(cpu) {
- smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
- cond_resched_tasks_rcu_qs();
- }
-
- /* Unconditionally decrement: no need to wake ourselves up. */
- atomic_dec(&oom_callback_count);
-
- return NOTIFY_OK;
-}
-
-static struct notifier_block rcu_oom_nb = {
- .notifier_call = rcu_oom_notify
-};
-
-static int __init rcu_register_oom_notifier(void)
-{
- register_oom_notifier(&rcu_oom_nb);
- return 0;
-}
-early_initcall(rcu_register_oom_notifier);
-
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
-
-#ifdef CONFIG_RCU_FAST_NO_HZ
-
-static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
-{
- struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
- unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
-
- sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
- rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
- ulong2long(nlpd),
- rdtp->all_lazy ? 'L' : '.',
- rdtp->tick_nohz_enabled_snap ? '.' : 'D');
-}
-
-#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
-
-static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
-{
- *cp = '\0';
-}
-
-#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
-
-/* Initiate the stall-info list. */
-static void print_cpu_stall_info_begin(void)
-{
- pr_cont("\n");
-}
-
-/*
- * Print out diagnostic information for the specified stalled CPU.
- *
- * If the specified CPU is aware of the current RCU grace period
- * (flavor specified by rsp), then print the number of scheduling
- * clock interrupts the CPU has taken during the time that it has
- * been aware. Otherwise, print the number of RCU grace periods
- * that this CPU is ignorant of, for example, "1" if the CPU was
- * aware of the previous grace period.
- *
- * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
- */
-static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
-{
- unsigned long delta;
- char fast_no_hz[72];
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_dynticks *rdtp = rdp->dynticks;
- char *ticks_title;
- unsigned long ticks_value;
-
- /*
- * We could be printing a lot while holding a spinlock. Avoid
- * triggering hard lockup.
- */
- touch_nmi_watchdog();
-
- ticks_value = rcu_seq_ctr(rsp->gp_seq - rdp->gp_seq);
- if (ticks_value) {
- ticks_title = "GPs behind";
- } else {
- ticks_title = "ticks this GP";
- ticks_value = rdp->ticks_this_gp;
- }
- print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
- delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
- pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
- cpu,
- "O."[!!cpu_online(cpu)],
- "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
- "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
- !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
- rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
- "!."[!delta],
- ticks_value, ticks_title,
- rcu_dynticks_snap(rdtp) & 0xfff,
- rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
- rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
- READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
- fast_no_hz);
-}
-
-/* Terminate the stall-info list. */
-static void print_cpu_stall_info_end(void)
-{
- pr_err("\t");
-}
-
-/* Zero ->ticks_this_gp for all flavors of RCU. */
-static void zero_cpu_stall_ticks(struct rcu_data *rdp)
-{
- rdp->ticks_this_gp = 0;
- rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
-}
-
-/* Increment ->ticks_this_gp for all flavors of RCU. */
-static void increment_cpu_stall_ticks(void)
-{
- struct rcu_state *rsp;
-
- for_each_rcu_flavor(rsp)
- raw_cpu_inc(rsp->rda->ticks_this_gp);
-}
#ifdef CONFIG_RCU_NOCB_CPU
/*
* Offload callback processing from the boot-time-specified set of CPUs
- * specified by rcu_nocb_mask. For each CPU in the set, there is a
- * kthread created that pulls the callbacks from the corresponding CPU,
- * waits for a grace period to elapse, and invokes the callbacks.
- * The no-CBs CPUs do a wake_up() on their kthread when they insert
- * a callback into any empty list, unless the rcu_nocb_poll boot parameter
- * has been specified, in which case each kthread actively polls its
- * CPU. (Which isn't so great for energy efficiency, but which does
- * reduce RCU's overhead on that CPU.)
+ * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
+ * created that pull the callbacks from the corresponding CPU, wait for
+ * a grace period to elapse, and invoke the callbacks. These kthreads
+ * are organized into GP kthreads, which manage incoming callbacks, wait for
+ * grace periods, and awaken CB kthreads, and the CB kthreads, which only
+ * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
+ * do a wake_up() on their GP kthread when they insert a callback into any
+ * empty list, unless the rcu_nocb_poll boot parameter has been specified,
+ * in which case each kthread actively polls its CPU. (Which isn't so great
+ * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
*
* This is intended to be used in conjunction with Frederic Weisbecker's
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
* running CPU-bound user-mode computations.
*
- * Offloading of callback processing could also in theory be used as
- * an energy-efficiency measure because CPUs with no RCU callbacks
- * queued are more aggressive about entering dyntick-idle mode.
+ * Offloading of callbacks can also be used as an energy-efficiency
+ * measure because CPUs with no RCU callbacks queued are more aggressive
+ * about entering dyntick-idle mode.
*/
-/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
+/*
+ * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
+ * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
+ * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
+ * given, a warning is emitted and all CPUs are offloaded.
+ */
static int __init rcu_nocb_setup(char *str)
{
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
- cpulist_parse(str, rcu_nocb_mask);
+ if (!strcasecmp(str, "all"))
+ cpumask_setall(rcu_nocb_mask);
+ else
+ if (cpulist_parse(str, rcu_nocb_mask)) {
+ pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
+ cpumask_setall(rcu_nocb_mask);
+ }
return 1;
}
__setup("rcu_nocbs=", rcu_nocb_setup);
@@ -1878,6 +1489,117 @@
return 0;
}
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
+
+/*
+ * Don't bother bypassing ->cblist if the call_rcu() rate is low.
+ * After all, the main point of bypassing is to avoid lock contention
+ * on ->nocb_lock, which only can happen at high call_rcu() rates.
+ */
+int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
+module_param(nocb_nobypass_lim_per_jiffy, int, 0);
+
+/*
+ * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
+ * lock isn't immediately available, increment ->nocb_lock_contended to
+ * flag the contention.
+ */
+static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
+ __acquires(&rdp->nocb_bypass_lock)
+{
+ lockdep_assert_irqs_disabled();
+ if (raw_spin_trylock(&rdp->nocb_bypass_lock))
+ return;
+ atomic_inc(&rdp->nocb_lock_contended);
+ WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
+ smp_mb__after_atomic(); /* atomic_inc() before lock. */
+ raw_spin_lock(&rdp->nocb_bypass_lock);
+ smp_mb__before_atomic(); /* atomic_dec() after lock. */
+ atomic_dec(&rdp->nocb_lock_contended);
+}
+
+/*
+ * Spinwait until the specified rcu_data structure's ->nocb_lock is
+ * not contended. Please note that this is extremely special-purpose,
+ * relying on the fact that at most two kthreads and one CPU contend for
+ * this lock, and also that the two kthreads are guaranteed to have frequent
+ * grace-period-duration time intervals between successive acquisitions
+ * of the lock. This allows us to use an extremely simple throttling
+ * mechanism, and further to apply it only to the CPU doing floods of
+ * call_rcu() invocations. Don't try this at home!
+ */
+static void rcu_nocb_wait_contended(struct rcu_data *rdp)
+{
+ WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
+ while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
+ cpu_relax();
+}
+
+/*
+ * Conditionally acquire the specified rcu_data structure's
+ * ->nocb_bypass_lock.
+ */
+static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
+{
+ lockdep_assert_irqs_disabled();
+ return raw_spin_trylock(&rdp->nocb_bypass_lock);
+}
+
+/*
+ * Release the specified rcu_data structure's ->nocb_bypass_lock.
+ */
+static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
+ __releases(&rdp->nocb_bypass_lock)
+{
+ lockdep_assert_irqs_disabled();
+ raw_spin_unlock(&rdp->nocb_bypass_lock);
+}
+
+/*
+ * Acquire the specified rcu_data structure's ->nocb_lock, but only
+ * if it corresponds to a no-CBs CPU.
+ */
+static void rcu_nocb_lock(struct rcu_data *rdp)
+{
+ lockdep_assert_irqs_disabled();
+ if (!rcu_segcblist_is_offloaded(&rdp->cblist))
+ return;
+ raw_spin_lock(&rdp->nocb_lock);
+}
+
+/*
+ * Release the specified rcu_data structure's ->nocb_lock, but only
+ * if it corresponds to a no-CBs CPU.
+ */
+static void rcu_nocb_unlock(struct rcu_data *rdp)
+{
+ if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
+ lockdep_assert_irqs_disabled();
+ raw_spin_unlock(&rdp->nocb_lock);
+ }
+}
+
+/*
+ * Release the specified rcu_data structure's ->nocb_lock and restore
+ * interrupts, but only if it corresponds to a no-CBs CPU.
+ */
+static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
+ unsigned long flags)
+{
+ if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
+ lockdep_assert_irqs_disabled();
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ } else {
+ local_irq_restore(flags);
+ }
+}
+
+/* Lockdep check that ->cblist may be safely accessed. */
+static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
+{
+ lockdep_assert_irqs_disabled();
+ if (rcu_segcblist_is_offloaded(&rdp->cblist))
+ lockdep_assert_held(&rdp->nocb_lock);
+}
/*
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
@@ -1908,442 +1630,523 @@
}
/*
- * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
+ * Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
* and this function releases it.
*/
-static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
- unsigned long flags)
+static void wake_nocb_gp(struct rcu_data *rdp, bool force,
+ unsigned long flags)
__releases(rdp->nocb_lock)
{
- struct rcu_data *rdp_leader = rdp->nocb_leader;
+ bool needwake = false;
+ struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
lockdep_assert_held(&rdp->nocb_lock);
- if (!READ_ONCE(rdp_leader->nocb_kthread)) {
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+ TPS("AlreadyAwake"));
+ rcu_nocb_unlock_irqrestore(rdp, flags);
return;
}
- if (rdp_leader->nocb_leader_sleep || force) {
- /* Prior smp_mb__after_atomic() orders against prior enqueue. */
- WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
+
+ if (READ_ONCE(rdp->nocb_defer_wakeup) > RCU_NOCB_WAKE_NOT) {
+ WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
del_timer(&rdp->nocb_timer);
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
- smp_mb(); /* ->nocb_leader_sleep before swake_up_one(). */
- swake_up_one(&rdp_leader->nocb_wq);
- } else {
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
}
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
+ if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
+ WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
+ needwake = true;
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
+ }
+ raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
+ if (needwake)
+ wake_up_process(rdp_gp->nocb_gp_kthread);
}
/*
- * Kick the leader kthread for this NOCB group, but caller has not
- * acquired locks.
+ * Arrange to wake the GP kthread for this NOCB group at some future
+ * time when it is safe to do so.
*/
-static void wake_nocb_leader(struct rcu_data *rdp, bool force)
+static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
+ const char *reason)
{
- unsigned long flags;
-
- raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
- __wake_nocb_leader(rdp, force, flags);
-}
-
-/*
- * Arrange to wake the leader kthread for this NOCB group at some
- * future time when it is safe to do so.
- */
-static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
- const char *reason)
-{
- unsigned long flags;
-
- raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
mod_timer(&rdp->nocb_timer, jiffies + 1);
- WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason);
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ if (rdp->nocb_defer_wakeup < waketype)
+ WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
}
/*
- * Does the specified CPU need an RCU callback for the specified flavor
- * of rcu_barrier()?
+ * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
+ * However, if there is a callback to be enqueued and if ->nocb_bypass
+ * proves to be initially empty, just return false because the no-CB GP
+ * kthread may need to be awakened in this case.
+ *
+ * Note that this function always returns true if rhp is NULL.
*/
-static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
+ unsigned long j)
{
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- unsigned long ret;
-#ifdef CONFIG_PROVE_RCU
- struct rcu_head *rhp;
-#endif /* #ifdef CONFIG_PROVE_RCU */
+ struct rcu_cblist rcl;
- /*
- * Check count of all no-CBs callbacks awaiting invocation.
- * There needs to be a barrier before this function is called,
- * but associated with a prior determination that no more
- * callbacks would be posted. In the worst case, the first
- * barrier in _rcu_barrier() suffices (but the caller cannot
- * necessarily rely on this, not a substitute for the caller
- * getting the concurrency design right!). There must also be
- * a barrier between the following load an posting of a callback
- * (if a callback is in fact needed). This is associated with an
- * atomic_inc() in the caller.
- */
- ret = atomic_long_read(&rdp->nocb_q_count);
-
-#ifdef CONFIG_PROVE_RCU
- rhp = READ_ONCE(rdp->nocb_head);
- if (!rhp)
- rhp = READ_ONCE(rdp->nocb_gp_head);
- if (!rhp)
- rhp = READ_ONCE(rdp->nocb_follower_head);
-
- /* Having no rcuo kthread but CBs after scheduler starts is bad! */
- if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
- rcu_scheduler_fully_active) {
- /* RCU callback enqueued before CPU first came online??? */
- pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
- cpu, rhp->func);
- WARN_ON_ONCE(1);
+ WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist));
+ rcu_lockdep_assert_cblist_protected(rdp);
+ lockdep_assert_held(&rdp->nocb_bypass_lock);
+ if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
+ raw_spin_unlock(&rdp->nocb_bypass_lock);
+ return false;
}
-#endif /* #ifdef CONFIG_PROVE_RCU */
-
- return !!ret;
+ /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
+ if (rhp)
+ rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
+ rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
+ rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
+ WRITE_ONCE(rdp->nocb_bypass_first, j);
+ rcu_nocb_bypass_unlock(rdp);
+ return true;
}
/*
- * Enqueue the specified string of rcu_head structures onto the specified
- * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
- * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
- * counts are supplied by rhcount and rhcount_lazy.
+ * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
+ * However, if there is a callback to be enqueued and if ->nocb_bypass
+ * proves to be initially empty, just return false because the no-CB GP
+ * kthread may need to be awakened in this case.
+ *
+ * Note that this function always returns true if rhp is NULL.
+ */
+static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
+ unsigned long j)
+{
+ if (!rcu_segcblist_is_offloaded(&rdp->cblist))
+ return true;
+ rcu_lockdep_assert_cblist_protected(rdp);
+ rcu_nocb_bypass_lock(rdp);
+ return rcu_nocb_do_flush_bypass(rdp, rhp, j);
+}
+
+/*
+ * If the ->nocb_bypass_lock is immediately available, flush the
+ * ->nocb_bypass queue into ->cblist.
+ */
+static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
+{
+ rcu_lockdep_assert_cblist_protected(rdp);
+ if (!rcu_segcblist_is_offloaded(&rdp->cblist) ||
+ !rcu_nocb_bypass_trylock(rdp))
+ return;
+ WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
+}
+
+/*
+ * See whether it is appropriate to use the ->nocb_bypass list in order
+ * to control contention on ->nocb_lock. A limited number of direct
+ * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
+ * is non-empty, further callbacks must be placed into ->nocb_bypass,
+ * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
+ * back to direct use of ->cblist. However, ->nocb_bypass should not be
+ * used if ->cblist is empty, because otherwise callbacks can be stranded
+ * on ->nocb_bypass because we cannot count on the current CPU ever again
+ * invoking call_rcu(). The general rule is that if ->nocb_bypass is
+ * non-empty, the corresponding no-CBs grace-period kthread must not be
+ * in an indefinite sleep state.
+ *
+ * Finally, it is not permitted to use the bypass during early boot,
+ * as doing so would confuse the auto-initialization code. Besides
+ * which, there is no point in worrying about lock contention while
+ * there is only one CPU in operation.
+ */
+static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
+ bool *was_alldone, unsigned long flags)
+{
+ unsigned long c;
+ unsigned long cur_gp_seq;
+ unsigned long j = jiffies;
+ long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+
+ if (!rcu_segcblist_is_offloaded(&rdp->cblist)) {
+ *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
+ return false; /* Not offloaded, no bypassing. */
+ }
+ lockdep_assert_irqs_disabled();
+
+ // Don't use ->nocb_bypass during early boot.
+ if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
+ rcu_nocb_lock(rdp);
+ WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
+ *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
+ return false;
+ }
+
+ // If we have advanced to a new jiffy, reset counts to allow
+ // moving back from ->nocb_bypass to ->cblist.
+ if (j == rdp->nocb_nobypass_last) {
+ c = rdp->nocb_nobypass_count + 1;
+ } else {
+ WRITE_ONCE(rdp->nocb_nobypass_last, j);
+ c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
+ if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
+ nocb_nobypass_lim_per_jiffy))
+ c = 0;
+ else if (c > nocb_nobypass_lim_per_jiffy)
+ c = nocb_nobypass_lim_per_jiffy;
+ }
+ WRITE_ONCE(rdp->nocb_nobypass_count, c);
+
+ // If there hasn't yet been all that many ->cblist enqueues
+ // this jiffy, tell the caller to enqueue onto ->cblist. But flush
+ // ->nocb_bypass first.
+ if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
+ rcu_nocb_lock(rdp);
+ *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
+ if (*was_alldone)
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+ TPS("FirstQ"));
+ WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
+ WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
+ return false; // Caller must enqueue the callback.
+ }
+
+ // If ->nocb_bypass has been used too long or is too full,
+ // flush ->nocb_bypass to ->cblist.
+ if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
+ ncbs >= qhimark) {
+ rcu_nocb_lock(rdp);
+ if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
+ *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
+ if (*was_alldone)
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+ TPS("FirstQ"));
+ WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
+ return false; // Caller must enqueue the callback.
+ }
+ if (j != rdp->nocb_gp_adv_time &&
+ rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
+ rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
+ rcu_advance_cbs_nowake(rdp->mynode, rdp);
+ rdp->nocb_gp_adv_time = j;
+ }
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ return true; // Callback already enqueued.
+ }
+
+ // We need to use the bypass.
+ rcu_nocb_wait_contended(rdp);
+ rcu_nocb_bypass_lock(rdp);
+ ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+ rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
+ rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
+ if (!ncbs) {
+ WRITE_ONCE(rdp->nocb_bypass_first, j);
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
+ }
+ rcu_nocb_bypass_unlock(rdp);
+ smp_mb(); /* Order enqueue before wake. */
+ if (ncbs) {
+ local_irq_restore(flags);
+ } else {
+ // No-CBs GP kthread might be indefinitely asleep, if so, wake.
+ rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
+ if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+ TPS("FirstBQwake"));
+ __call_rcu_nocb_wake(rdp, true, flags);
+ } else {
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+ TPS("FirstBQnoWake"));
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ }
+ }
+ return true; // Callback already enqueued.
+}
+
+/*
+ * Awaken the no-CBs grace-period kthead if needed, either due to it
+ * legitimately being asleep or due to overload conditions.
*
* If warranted, also wake up the kthread servicing this CPUs queues.
*/
-static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
- struct rcu_head *rhp,
- struct rcu_head **rhtp,
- int rhcount, int rhcount_lazy,
- unsigned long flags)
+static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
+ unsigned long flags)
+ __releases(rdp->nocb_lock)
{
- int len;
- struct rcu_head **old_rhpp;
+ unsigned long cur_gp_seq;
+ unsigned long j;
+ long len;
struct task_struct *t;
- /* Enqueue the callback on the nocb list and update counts. */
- atomic_long_add(rhcount, &rdp->nocb_q_count);
- /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
- old_rhpp = xchg(&rdp->nocb_tail, rhtp);
- WRITE_ONCE(*old_rhpp, rhp);
- atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
- smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
-
- /* If we are not being polled and there is a kthread, awaken it ... */
- t = READ_ONCE(rdp->nocb_kthread);
+ // If we are being polled or there is no kthread, just leave.
+ t = READ_ONCE(rdp->nocb_gp_kthread);
if (rcu_nocb_poll || !t) {
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("WakeNotPoll"));
+ rcu_nocb_unlock_irqrestore(rdp, flags);
return;
}
- len = atomic_long_read(&rdp->nocb_q_count);
- if (old_rhpp == &rdp->nocb_head) {
+ // Need to actually to a wakeup.
+ len = rcu_segcblist_n_cbs(&rdp->cblist);
+ if (was_alldone) {
+ rdp->qlen_last_fqs_check = len;
if (!irqs_disabled_flags(flags)) {
/* ... if queue was empty ... */
- wake_nocb_leader(rdp, false);
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ wake_nocb_gp(rdp, false, flags);
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("WakeEmpty"));
} else {
- wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
- TPS("WakeEmptyIsDeferred"));
+ wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
+ TPS("WakeEmptyIsDeferred"));
+ rcu_nocb_unlock_irqrestore(rdp, flags);
}
- rdp->qlen_last_fqs_check = 0;
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
/* ... or if many callbacks queued. */
- if (!irqs_disabled_flags(flags)) {
- wake_nocb_leader(rdp, true);
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
- TPS("WakeOvf"));
- } else {
- wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE_FORCE,
- TPS("WakeOvfIsDeferred"));
+ rdp->qlen_last_fqs_check = len;
+ j = jiffies;
+ if (j != rdp->nocb_gp_adv_time &&
+ rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
+ rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
+ rcu_advance_cbs_nowake(rdp->mynode, rdp);
+ rdp->nocb_gp_adv_time = j;
}
- rdp->qlen_last_fqs_check = LONG_MAX / 2;
+ smp_mb(); /* Enqueue before timer_pending(). */
+ if ((rdp->nocb_cb_sleep ||
+ !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
+ !timer_pending(&rdp->nocb_bypass_timer))
+ wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
+ TPS("WakeOvfIsDeferred"));
+ rcu_nocb_unlock_irqrestore(rdp, flags);
} else {
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
+ rcu_nocb_unlock_irqrestore(rdp, flags);
}
return;
}
-/*
- * This is a helper for __call_rcu(), which invokes this when the normal
- * callback queue is inoperable. If this is not a no-CBs CPU, this
- * function returns failure back to __call_rcu(), which can complain
- * appropriately.
- *
- * Otherwise, this function queues the callback where the corresponding
- * "rcuo" kthread can find it.
- */
-static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
- bool lazy, unsigned long flags)
+/* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */
+static void do_nocb_bypass_wakeup_timer(struct timer_list *t)
{
+ unsigned long flags;
+ struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer);
- if (!rcu_is_nocb_cpu(rdp->cpu))
- return false;
- __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
- if (__is_kfree_rcu_offset((unsigned long)rhp->func))
- trace_rcu_kfree_callback(rdp->rsp->name, rhp,
- (unsigned long)rhp->func,
- -atomic_long_read(&rdp->nocb_q_count_lazy),
- -atomic_long_read(&rdp->nocb_q_count));
- else
- trace_rcu_callback(rdp->rsp->name, rhp,
- -atomic_long_read(&rdp->nocb_q_count_lazy),
- -atomic_long_read(&rdp->nocb_q_count));
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
+ rcu_nocb_lock_irqsave(rdp, flags);
+ smp_mb__after_spinlock(); /* Timer expire before wakeup. */
+ __call_rcu_nocb_wake(rdp, true, flags);
+}
+
+/*
+ * No-CBs GP kthreads come here to wait for additional callbacks to show up
+ * or for grace periods to end.
+ */
+static void nocb_gp_wait(struct rcu_data *my_rdp)
+{
+ bool bypass = false;
+ long bypass_ncbs;
+ int __maybe_unused cpu = my_rdp->cpu;
+ unsigned long cur_gp_seq;
+ unsigned long flags;
+ bool gotcbs = false;
+ unsigned long j = jiffies;
+ bool needwait_gp = false; // This prevents actual uninitialized use.
+ bool needwake;
+ bool needwake_gp;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
+ bool wasempty = false;
/*
- * If called from an extended quiescent state with interrupts
- * disabled, invoke the RCU core in order to allow the idle-entry
- * deferred-wakeup check to function.
+ * Each pass through the following loop checks for CBs and for the
+ * nearest grace period (if any) to wait for next. The CB kthreads
+ * and the global grace-period kthread are awakened if needed.
*/
- if (irqs_disabled_flags(flags) &&
- !rcu_is_watching() &&
- cpu_online(smp_processor_id()))
- invoke_rcu_core();
+ WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
+ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
+ rcu_nocb_lock_irqsave(rdp, flags);
+ bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+ if (bypass_ncbs &&
+ (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
+ bypass_ncbs > 2 * qhimark)) {
+ // Bypass full or old, so flush it.
+ (void)rcu_nocb_try_flush_bypass(rdp, j);
+ bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+ } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ continue; /* No callbacks here, try next. */
+ }
+ if (bypass_ncbs) {
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+ TPS("Bypass"));
+ bypass = true;
+ }
+ rnp = rdp->mynode;
+ if (bypass) { // Avoid race with first bypass CB.
+ WRITE_ONCE(my_rdp->nocb_defer_wakeup,
+ RCU_NOCB_WAKE_NOT);
+ del_timer(&my_rdp->nocb_timer);
+ }
+ // Advance callbacks if helpful and low contention.
+ needwake_gp = false;
+ if (!rcu_segcblist_restempty(&rdp->cblist,
+ RCU_NEXT_READY_TAIL) ||
+ (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
+ rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
+ raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
+ needwake_gp = rcu_advance_cbs(rnp, rdp);
+ wasempty = rcu_segcblist_restempty(&rdp->cblist,
+ RCU_NEXT_READY_TAIL);
+ raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
+ }
+ // Need to wait on some grace period?
+ WARN_ON_ONCE(wasempty &&
+ !rcu_segcblist_restempty(&rdp->cblist,
+ RCU_NEXT_READY_TAIL));
+ if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
+ if (!needwait_gp ||
+ ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
+ wait_gp_seq = cur_gp_seq;
+ needwait_gp = true;
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+ TPS("NeedWaitGP"));
+ }
+ if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
+ needwake = rdp->nocb_cb_sleep;
+ WRITE_ONCE(rdp->nocb_cb_sleep, false);
+ smp_mb(); /* CB invocation -after- GP end. */
+ } else {
+ needwake = false;
+ }
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ if (needwake) {
+ swake_up_one(&rdp->nocb_cb_wq);
+ gotcbs = true;
+ }
+ if (needwake_gp)
+ rcu_gp_kthread_wake();
+ }
- return true;
+ my_rdp->nocb_gp_bypass = bypass;
+ my_rdp->nocb_gp_gp = needwait_gp;
+ my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
+ if (bypass && !rcu_nocb_poll) {
+ // At least one child with non-empty ->nocb_bypass, so set
+ // timer in order to avoid stranding its callbacks.
+ raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
+ mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
+ raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
+ }
+ if (rcu_nocb_poll) {
+ /* Polling, so trace if first poll in the series. */
+ if (gotcbs)
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
+ schedule_timeout_idle(1);
+ } else if (!needwait_gp) {
+ /* Wait for callbacks to appear. */
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
+ swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
+ !READ_ONCE(my_rdp->nocb_gp_sleep));
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
+ } else {
+ rnp = my_rdp->mynode;
+ trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
+ swait_event_interruptible_exclusive(
+ rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
+ rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
+ !READ_ONCE(my_rdp->nocb_gp_sleep));
+ trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
+ }
+ if (!rcu_nocb_poll) {
+ raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
+ if (bypass)
+ del_timer(&my_rdp->nocb_bypass_timer);
+ WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
+ raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
+ }
+ my_rdp->nocb_gp_seq = -1;
+ WARN_ON(signal_pending(current));
}
/*
- * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
- * not a no-CBs CPU.
+ * No-CBs grace-period-wait kthread. There is one of these per group
+ * of CPUs, but only once at least one CPU in that group has come online
+ * at least once since boot. This kthread checks for newly posted
+ * callbacks from any of the CPUs it is responsible for, waits for a
+ * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
+ * that then have callback-invocation work to do.
*/
-static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
- struct rcu_data *rdp,
- unsigned long flags)
+static int rcu_nocb_gp_kthread(void *arg)
{
- lockdep_assert_irqs_disabled();
- if (!rcu_is_nocb_cpu(smp_processor_id()))
- return false; /* Not NOCBs CPU, caller must migrate CBs. */
- __call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
- rcu_segcblist_tail(&rdp->cblist),
- rcu_segcblist_n_cbs(&rdp->cblist),
- rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags);
- rcu_segcblist_init(&rdp->cblist);
- rcu_segcblist_disable(&rdp->cblist);
- return true;
+ struct rcu_data *rdp = arg;
+
+ for (;;) {
+ WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
+ nocb_gp_wait(rdp);
+ cond_resched_tasks_rcu_qs();
+ }
+ return 0;
}
/*
- * If necessary, kick off a new grace period, and either way wait
- * for a subsequent grace period to complete.
+ * Invoke any ready callbacks from the corresponding no-CBs CPU,
+ * then, if there are no more, wait for more to appear.
*/
-static void rcu_nocb_wait_gp(struct rcu_data *rdp)
+static void nocb_cb_wait(struct rcu_data *rdp)
{
- unsigned long c;
- bool d;
+ unsigned long cur_gp_seq;
unsigned long flags;
- bool needwake;
+ bool needwake_gp = false;
struct rcu_node *rnp = rdp->mynode;
local_irq_save(flags);
- c = rcu_seq_snap(&rdp->rsp->gp_seq);
- if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
- local_irq_restore(flags);
- } else {
- raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- needwake = rcu_start_this_gp(rnp, rdp, c);
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- if (needwake)
- rcu_gp_kthread_wake(rdp->rsp);
+ rcu_momentary_dyntick_idle();
+ local_irq_restore(flags);
+ local_bh_disable();
+ rcu_do_batch(rdp);
+ local_bh_enable();
+ lockdep_assert_irqs_enabled();
+ rcu_nocb_lock_irqsave(rdp, flags);
+ if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
+ rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
+ raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
+ needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+ }
+ if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ if (needwake_gp)
+ rcu_gp_kthread_wake();
+ return;
}
- /*
- * Wait for the grace period. Do so interruptibly to avoid messing
- * up the load average.
- */
- trace_rcu_this_gp(rnp, rdp, c, TPS("StartWait"));
- for (;;) {
- swait_event_interruptible_exclusive(
- rnp->nocb_gp_wq[rcu_seq_ctr(c) & 0x1],
- (d = rcu_seq_done(&rnp->gp_seq, c)));
- if (likely(d))
- break;
- WARN_ON(signal_pending(current));
- trace_rcu_this_gp(rnp, rdp, c, TPS("ResumeWait"));
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
+ WRITE_ONCE(rdp->nocb_cb_sleep, true);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ if (needwake_gp)
+ rcu_gp_kthread_wake();
+ swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
+ !READ_ONCE(rdp->nocb_cb_sleep));
+ if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */
+ /* ^^^ Ensure CB invocation follows _sleep test. */
+ return;
}
- trace_rcu_this_gp(rnp, rdp, c, TPS("EndWait"));
- smp_mb(); /* Ensure that CB invocation happens after GP end. */
+ WARN_ON(signal_pending(current));
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
}
/*
- * Leaders come here to wait for additional callbacks to show up.
- * This function does not return until callbacks appear.
+ * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
+ * nocb_cb_wait() to do the dirty work.
*/
-static void nocb_leader_wait(struct rcu_data *my_rdp)
+static int rcu_nocb_cb_kthread(void *arg)
{
- bool firsttime = true;
- unsigned long flags;
- bool gotcbs;
- struct rcu_data *rdp;
- struct rcu_head **tail;
-
-wait_again:
-
- /* Wait for callbacks to appear. */
- if (!rcu_nocb_poll) {
- trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep"));
- swait_event_interruptible_exclusive(my_rdp->nocb_wq,
- !READ_ONCE(my_rdp->nocb_leader_sleep));
- raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
- my_rdp->nocb_leader_sleep = true;
- WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
- del_timer(&my_rdp->nocb_timer);
- raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
- } else if (firsttime) {
- firsttime = false; /* Don't drown trace log with "Poll"! */
- trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll"));
- }
-
- /*
- * Each pass through the following loop checks a follower for CBs.
- * We are our own first follower. Any CBs found are moved to
- * nocb_gp_head, where they await a grace period.
- */
- gotcbs = false;
- smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
- for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
- rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
- if (!rdp->nocb_gp_head)
- continue; /* No CBs here, try next follower. */
-
- /* Move callbacks to wait-for-GP list, which is empty. */
- WRITE_ONCE(rdp->nocb_head, NULL);
- rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
- gotcbs = true;
- }
-
- /* No callbacks? Sleep a bit if polling, and go retry. */
- if (unlikely(!gotcbs)) {
- WARN_ON(signal_pending(current));
- if (rcu_nocb_poll) {
- schedule_timeout_interruptible(1);
- } else {
- trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
- TPS("WokeEmpty"));
- }
- goto wait_again;
- }
-
- /* Wait for one grace period. */
- rcu_nocb_wait_gp(my_rdp);
-
- /* Each pass through the following loop wakes a follower, if needed. */
- for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
- if (!rcu_nocb_poll &&
- READ_ONCE(rdp->nocb_head) &&
- READ_ONCE(my_rdp->nocb_leader_sleep)) {
- raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
- my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
- raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
- }
- if (!rdp->nocb_gp_head)
- continue; /* No CBs, so no need to wake follower. */
-
- /* Append callbacks to follower's "done" list. */
- raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
- tail = rdp->nocb_follower_tail;
- rdp->nocb_follower_tail = rdp->nocb_gp_tail;
- *tail = rdp->nocb_gp_head;
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
- if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
- /* List was empty, so wake up the follower. */
- swake_up_one(&rdp->nocb_wq);
- }
- }
-
- /* If we (the leader) don't have CBs, go wait some more. */
- if (!my_rdp->nocb_follower_head)
- goto wait_again;
-}
-
-/*
- * Followers come here to wait for additional callbacks to show up.
- * This function does not return until callbacks appear.
- */
-static void nocb_follower_wait(struct rcu_data *rdp)
-{
- for (;;) {
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep"));
- swait_event_interruptible_exclusive(rdp->nocb_wq,
- READ_ONCE(rdp->nocb_follower_head));
- if (smp_load_acquire(&rdp->nocb_follower_head)) {
- /* ^^^ Ensure CB invocation follows _head test. */
- return;
- }
- WARN_ON(signal_pending(current));
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty"));
- }
-}
-
-/*
- * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
- * callbacks queued by the corresponding no-CBs CPU, however, there is
- * an optional leader-follower relationship so that the grace-period
- * kthreads don't have to do quite so many wakeups.
- */
-static int rcu_nocb_kthread(void *arg)
-{
- int c, cl;
- unsigned long flags;
- struct rcu_head *list;
- struct rcu_head *next;
- struct rcu_head **tail;
struct rcu_data *rdp = arg;
- /* Each pass through this loop invokes one batch of callbacks */
+ // Each pass through this loop does one callback batch, and,
+ // if there are no more ready callbacks, waits for them.
for (;;) {
- /* Wait for callbacks. */
- if (rdp->nocb_leader == rdp)
- nocb_leader_wait(rdp);
- else
- nocb_follower_wait(rdp);
-
- /* Pull the ready-to-invoke callbacks onto local list. */
- raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
- list = rdp->nocb_follower_head;
- rdp->nocb_follower_head = NULL;
- tail = rdp->nocb_follower_tail;
- rdp->nocb_follower_tail = &rdp->nocb_follower_head;
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
- BUG_ON(!list);
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty"));
-
- /* Each pass through the following loop invokes a callback. */
- trace_rcu_batch_start(rdp->rsp->name,
- atomic_long_read(&rdp->nocb_q_count_lazy),
- atomic_long_read(&rdp->nocb_q_count), -1);
- c = cl = 0;
- while (list) {
- next = list->next;
- /* Wait for enqueuing to complete, if needed. */
- while (next == NULL && &list->next != tail) {
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
- TPS("WaitQueue"));
- schedule_timeout_interruptible(1);
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
- TPS("WokeQueue"));
- next = list->next;
- }
- debug_rcu_head_unqueue(list);
- local_bh_disable();
- if (__rcu_reclaim(rdp->rsp->name, list))
- cl++;
- c++;
- local_bh_enable();
- cond_resched_tasks_rcu_qs();
- list = next;
- }
- trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
- smp_mb__before_atomic(); /* _add after CB invocation. */
- atomic_long_add(-c, &rdp->nocb_q_count);
- atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
+ nocb_cb_wait(rdp);
+ cond_resched_tasks_rcu_qs();
}
return 0;
}
@@ -2360,15 +2163,14 @@
unsigned long flags;
int ndw;
- raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+ rcu_nocb_lock_irqsave(rdp, flags);
if (!rcu_nocb_need_deferred_wakeup(rdp)) {
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
return;
}
ndw = READ_ONCE(rdp->nocb_defer_wakeup);
- WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
- __wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
- trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
+ wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
}
/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
@@ -2390,11 +2192,16 @@
do_nocb_deferred_wakeup_common(rdp);
}
+void rcu_nocb_flush_deferred_wakeup(void)
+{
+ do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
+}
+
void __init rcu_init_nohz(void)
{
int cpu;
bool need_rcu_nocb_mask = false;
- struct rcu_state *rsp;
+ struct rcu_data *rdp;
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
@@ -2428,82 +2235,73 @@
if (rcu_nocb_poll)
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
- for_each_rcu_flavor(rsp) {
- for_each_cpu(cpu, rcu_nocb_mask)
- init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
- rcu_organize_nocb_kthreads(rsp);
+ for_each_cpu(cpu, rcu_nocb_mask) {
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ if (rcu_segcblist_empty(&rdp->cblist))
+ rcu_segcblist_init(&rdp->cblist);
+ rcu_segcblist_offload(&rdp->cblist);
}
+ rcu_organize_nocb_kthreads();
}
/* Initialize per-rcu_data variables for no-CBs CPUs. */
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
- rdp->nocb_tail = &rdp->nocb_head;
- init_swait_queue_head(&rdp->nocb_wq);
- rdp->nocb_follower_tail = &rdp->nocb_follower_head;
+ init_swait_queue_head(&rdp->nocb_cb_wq);
+ init_swait_queue_head(&rdp->nocb_gp_wq);
raw_spin_lock_init(&rdp->nocb_lock);
+ raw_spin_lock_init(&rdp->nocb_bypass_lock);
+ raw_spin_lock_init(&rdp->nocb_gp_lock);
timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
+ timer_setup(&rdp->nocb_bypass_timer, do_nocb_bypass_wakeup_timer, 0);
+ rcu_cblist_init(&rdp->nocb_bypass);
}
/*
* If the specified CPU is a no-CBs CPU that does not already have its
- * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
- * brought online out of order, this can require re-organizing the
- * leader-follower relationships.
+ * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
+ * for this CPU's group has not yet been created, spawn it as well.
*/
-static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
+static void rcu_spawn_one_nocb_kthread(int cpu)
{
- struct rcu_data *rdp;
- struct rcu_data *rdp_last;
- struct rcu_data *rdp_old_leader;
- struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ struct rcu_data *rdp_gp;
struct task_struct *t;
/*
* If this isn't a no-CBs CPU or if it already has an rcuo kthread,
* then nothing to do.
*/
- if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
+ if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
return;
- /* If we didn't spawn the leader first, reorganize! */
- rdp_old_leader = rdp_spawn->nocb_leader;
- if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
- rdp_last = NULL;
- rdp = rdp_old_leader;
- do {
- rdp->nocb_leader = rdp_spawn;
- if (rdp_last && rdp != rdp_spawn)
- rdp_last->nocb_next_follower = rdp;
- if (rdp == rdp_spawn) {
- rdp = rdp->nocb_next_follower;
- } else {
- rdp_last = rdp;
- rdp = rdp->nocb_next_follower;
- rdp_last->nocb_next_follower = NULL;
- }
- } while (rdp);
- rdp_spawn->nocb_next_follower = rdp_old_leader;
+ /* If we didn't spawn the GP kthread first, reorganize! */
+ rdp_gp = rdp->nocb_gp_rdp;
+ if (!rdp_gp->nocb_gp_kthread) {
+ t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
+ "rcuog/%d", rdp_gp->cpu);
+ if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
+ return;
+ WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
}
- /* Spawn the kthread for this CPU and RCU flavor. */
- t = kthread_run(rcu_nocb_kthread, rdp_spawn,
- "rcuo%c/%d", rsp->abbr, cpu);
- BUG_ON(IS_ERR(t));
- WRITE_ONCE(rdp_spawn->nocb_kthread, t);
+ /* Spawn the kthread for this CPU. */
+ t = kthread_run(rcu_nocb_cb_kthread, rdp,
+ "rcuo%c/%d", rcu_state.abbr, cpu);
+ if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
+ return;
+ WRITE_ONCE(rdp->nocb_cb_kthread, t);
+ WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
}
/*
* If the specified CPU is a no-CBs CPU that does not already have its
- * rcuo kthreads, spawn them.
+ * rcuo kthread, spawn it.
*/
-static void rcu_spawn_all_nocb_kthreads(int cpu)
+static void rcu_spawn_cpu_nocb_kthread(int cpu)
{
- struct rcu_state *rsp;
-
if (rcu_scheduler_fully_active)
- for_each_rcu_flavor(rsp)
- rcu_spawn_one_nocb_kthread(rsp, cpu);
+ rcu_spawn_one_nocb_kthread(cpu);
}
/*
@@ -2517,30 +2315,33 @@
int cpu;
for_each_online_cpu(cpu)
- rcu_spawn_all_nocb_kthreads(cpu);
+ rcu_spawn_cpu_nocb_kthread(cpu);
}
-/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
-static int rcu_nocb_leader_stride = -1;
-module_param(rcu_nocb_leader_stride, int, 0444);
+/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
+static int rcu_nocb_gp_stride = -1;
+module_param(rcu_nocb_gp_stride, int, 0444);
/*
- * Initialize leader-follower relationships for all no-CBs CPU.
+ * Initialize GP-CB relationships for all no-CBs CPU.
*/
-static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
+static void __init rcu_organize_nocb_kthreads(void)
{
int cpu;
- int ls = rcu_nocb_leader_stride;
- int nl = 0; /* Next leader. */
+ bool firsttime = true;
+ bool gotnocbs = false;
+ bool gotnocbscbs = true;
+ int ls = rcu_nocb_gp_stride;
+ int nl = 0; /* Next GP kthread. */
struct rcu_data *rdp;
- struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
+ struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
struct rcu_data *rdp_prev = NULL;
if (!cpumask_available(rcu_nocb_mask))
return;
if (ls == -1) {
- ls = int_sqrt(nr_cpu_ids);
- rcu_nocb_leader_stride = ls;
+ ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
+ rcu_nocb_gp_stride = ls;
}
/*
@@ -2549,47 +2350,142 @@
* we will spawn the needed set of rcu_nocb_kthread() kthreads.
*/
for_each_cpu(cpu, rcu_nocb_mask) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
+ rdp = per_cpu_ptr(&rcu_data, cpu);
if (rdp->cpu >= nl) {
- /* New leader, set up for followers & next leader. */
+ /* New GP kthread, set up for CBs & next GP. */
+ gotnocbs = true;
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
- rdp->nocb_leader = rdp;
- rdp_leader = rdp;
+ rdp->nocb_gp_rdp = rdp;
+ rdp_gp = rdp;
+ if (dump_tree) {
+ if (!firsttime)
+ pr_cont("%s\n", gotnocbscbs
+ ? "" : " (self only)");
+ gotnocbscbs = false;
+ firsttime = false;
+ pr_alert("%s: No-CB GP kthread CPU %d:",
+ __func__, cpu);
+ }
} else {
- /* Another follower, link to previous leader. */
- rdp->nocb_leader = rdp_leader;
- rdp_prev->nocb_next_follower = rdp;
+ /* Another CB kthread, link to previous GP kthread. */
+ gotnocbscbs = true;
+ rdp->nocb_gp_rdp = rdp_gp;
+ rdp_prev->nocb_next_cb_rdp = rdp;
+ if (dump_tree)
+ pr_cont(" %d", cpu);
}
rdp_prev = rdp;
}
+ if (gotnocbs && dump_tree)
+ pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
}
-/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
-static bool init_nocb_callback_list(struct rcu_data *rdp)
+/*
+ * Bind the current task to the offloaded CPUs. If there are no offloaded
+ * CPUs, leave the task unbound. Splat if the bind attempt fails.
+ */
+void rcu_bind_current_to_nocb(void)
{
- if (!rcu_is_nocb_cpu(rdp->cpu))
- return false;
+ if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
+ WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
+}
+EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
- /* If there are early-boot callbacks, move them to nocb lists. */
- if (!rcu_segcblist_empty(&rdp->cblist)) {
- rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
- rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
- atomic_long_set(&rdp->nocb_q_count,
- rcu_segcblist_n_cbs(&rdp->cblist));
- atomic_long_set(&rdp->nocb_q_count_lazy,
- rcu_segcblist_n_lazy_cbs(&rdp->cblist));
- rcu_segcblist_init(&rdp->cblist);
- }
- rcu_segcblist_disable(&rdp->cblist);
- return true;
+/*
+ * Dump out nocb grace-period kthread state for the specified rcu_data
+ * structure.
+ */
+static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
+{
+ struct rcu_node *rnp = rdp->mynode;
+
+ pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
+ rdp->cpu,
+ "kK"[!!rdp->nocb_gp_kthread],
+ "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
+ "dD"[!!rdp->nocb_defer_wakeup],
+ "tT"[timer_pending(&rdp->nocb_timer)],
+ "bB"[timer_pending(&rdp->nocb_bypass_timer)],
+ "sS"[!!rdp->nocb_gp_sleep],
+ ".W"[swait_active(&rdp->nocb_gp_wq)],
+ ".W"[swait_active(&rnp->nocb_gp_wq[0])],
+ ".W"[swait_active(&rnp->nocb_gp_wq[1])],
+ ".B"[!!rdp->nocb_gp_bypass],
+ ".G"[!!rdp->nocb_gp_gp],
+ (long)rdp->nocb_gp_seq,
+ rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
+}
+
+/* Dump out nocb kthread state for the specified rcu_data structure. */
+static void show_rcu_nocb_state(struct rcu_data *rdp)
+{
+ struct rcu_segcblist *rsclp = &rdp->cblist;
+ bool waslocked;
+ bool wastimer;
+ bool wassleep;
+
+ if (rdp->nocb_gp_rdp == rdp)
+ show_rcu_nocb_gp_state(rdp);
+
+ pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
+ rdp->cpu, rdp->nocb_gp_rdp->cpu,
+ "kK"[!!rdp->nocb_cb_kthread],
+ "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
+ "cC"[!!atomic_read(&rdp->nocb_lock_contended)],
+ "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
+ "sS"[!!rdp->nocb_cb_sleep],
+ ".W"[swait_active(&rdp->nocb_cb_wq)],
+ jiffies - rdp->nocb_bypass_first,
+ jiffies - rdp->nocb_nobypass_last,
+ rdp->nocb_nobypass_count,
+ ".D"[rcu_segcblist_ready_cbs(rsclp)],
+ ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
+ ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
+ ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
+ ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
+ rcu_segcblist_n_cbs(&rdp->cblist));
+
+ /* It is OK for GP kthreads to have GP state. */
+ if (rdp->nocb_gp_rdp == rdp)
+ return;
+
+ waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
+ wastimer = timer_pending(&rdp->nocb_bypass_timer);
+ wassleep = swait_active(&rdp->nocb_gp_wq);
+ if (!rdp->nocb_gp_sleep && !waslocked && !wastimer && !wassleep)
+ return; /* Nothing untowards. */
+
+ pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c%c %c\n",
+ "lL"[waslocked],
+ "dD"[!!rdp->nocb_defer_wakeup],
+ "tT"[wastimer],
+ "sS"[!!rdp->nocb_gp_sleep],
+ ".W"[wassleep]);
}
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
-static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+/* No ->nocb_lock to acquire. */
+static void rcu_nocb_lock(struct rcu_data *rdp)
{
- WARN_ON_ONCE(1); /* Should be dead code. */
- return false;
+}
+
+/* No ->nocb_lock to release. */
+static void rcu_nocb_unlock(struct rcu_data *rdp)
+{
+}
+
+/* No ->nocb_lock to release. */
+static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
+ unsigned long flags)
+{
+ local_irq_restore(flags);
+}
+
+/* Lockdep check that ->cblist may be safely accessed. */
+static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
+{
+ lockdep_assert_irqs_disabled();
}
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
@@ -2605,17 +2501,22 @@
{
}
-static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
- bool lazy, unsigned long flags)
+static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
+ unsigned long j)
+{
+ return true;
+}
+
+static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
+ bool *was_alldone, unsigned long flags)
{
return false;
}
-static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
- struct rcu_data *rdp,
- unsigned long flags)
+static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
+ unsigned long flags)
{
- return false;
+ WARN_ON_ONCE(1); /* Should be dead code! */
}
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
@@ -2631,7 +2532,7 @@
{
}
-static void rcu_spawn_all_nocb_kthreads(int cpu)
+static void rcu_spawn_cpu_nocb_kthread(int cpu)
{
}
@@ -2639,9 +2540,8 @@
{
}
-static bool init_nocb_callback_list(struct rcu_data *rdp)
+static void show_rcu_nocb_state(struct rcu_data *rdp)
{
- return false;
}
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
@@ -2655,12 +2555,12 @@
* This code relies on the fact that all NO_HZ_FULL CPUs are also
* CONFIG_RCU_NOCB_CPU CPUs.
*/
-static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
+static bool rcu_nohz_full_cpu(void)
{
#ifdef CONFIG_NO_HZ_FULL
if (tick_nohz_full_cpu(smp_processor_id()) &&
- (!rcu_gp_in_progress(rsp) ||
- ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ)))
+ (!rcu_gp_in_progress() ||
+ time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
return true;
#endif /* #ifdef CONFIG_NO_HZ_FULL */
return false;
@@ -2677,7 +2577,7 @@
}
/* Record the current task on dyntick-idle entry. */
-static void rcu_dynticks_task_enter(void)
+static __always_inline void rcu_dynticks_task_enter(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
@@ -2685,9 +2585,27 @@
}
/* Record no current task on dyntick-idle exit. */
-static void rcu_dynticks_task_exit(void)
+static __always_inline void rcu_dynticks_task_exit(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}
+
+/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
+static __always_inline void rcu_dynticks_task_trace_enter(void)
+{
+#ifdef CONFIG_TASKS_TRACE_RCU
+ if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
+ current->trc_reader_special.b.need_mb = true;
+#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
+}
+
+/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
+static __always_inline void rcu_dynticks_task_trace_exit(void)
+{
+#ifdef CONFIG_TASKS_TRACE_RCU
+ if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
+ current->trc_reader_special.b.need_mb = false;
+#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
+}
--
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