/* 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.
|
*
|
* Copyright Red Hat, 2009
|
* Copyright IBM Corporation, 2009
|
*
|
* Author: Ingo Molnar <mingo@elte.hu>
|
* Paul E. McKenney <paulmck@linux.ibm.com>
|
*/
|
|
#include "../locking/rtmutex_common.h"
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
|
static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
|
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
/*
|
* Check the RCU kernel configuration parameters and print informative
|
* messages about anything out of the ordinary.
|
*/
|
static void __init rcu_bootup_announce_oddness(void)
|
{
|
if (IS_ENABLED(CONFIG_RCU_TRACE))
|
pr_info("\tRCU event tracing is enabled.\n");
|
if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
|
(!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
|
pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
|
RCU_FANOUT);
|
if (rcu_fanout_exact)
|
pr_info("\tHierarchical RCU autobalancing is disabled.\n");
|
if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
|
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)
|
pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
|
RCU_FANOUT_LEAF);
|
if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
|
pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
|
rcu_fanout_leaf);
|
if (nr_cpu_ids != NR_CPUS)
|
pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
|
#ifdef CONFIG_RCU_BOOST
|
pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
|
kthread_prio, CONFIG_RCU_BOOST_DELAY);
|
#endif
|
if (blimit != DEFAULT_RCU_BLIMIT)
|
pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
|
if (qhimark != DEFAULT_RCU_QHIMARK)
|
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))
|
pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
|
if (gp_preinit_delay)
|
pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
|
if (gp_init_delay)
|
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();
|
}
|
|
#ifdef CONFIG_PREEMPT_RCU
|
|
static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
|
static void rcu_read_unlock_special(struct task_struct *t);
|
|
/*
|
* Tell them what RCU they are running.
|
*/
|
static void __init rcu_bootup_announce(void)
|
{
|
pr_info("Preemptible hierarchical RCU implementation.\n");
|
rcu_bootup_announce_oddness();
|
}
|
|
/* Flags for rcu_preempt_ctxt_queue() decision table. */
|
#define RCU_GP_TASKS 0x8
|
#define RCU_EXP_TASKS 0x4
|
#define RCU_GP_BLKD 0x2
|
#define RCU_EXP_BLKD 0x1
|
|
/*
|
* Queues a task preempted within an RCU-preempt read-side critical
|
* section into the appropriate location within the ->blkd_tasks list,
|
* depending on the states of any ongoing normal and expedited grace
|
* periods. The ->gp_tasks pointer indicates which element the normal
|
* grace period is waiting on (NULL if none), and the ->exp_tasks pointer
|
* indicates which element the expedited grace period is waiting on (again,
|
* NULL if none). If a grace period is waiting on a given element in the
|
* ->blkd_tasks list, it also waits on all subsequent elements. Thus,
|
* adding a task to the tail of the list blocks any grace period that is
|
* already waiting on one of the elements. In contrast, adding a task
|
* to the head of the list won't block any grace period that is already
|
* waiting on one of the elements.
|
*
|
* This queuing is imprecise, and can sometimes make an ongoing grace
|
* period wait for a task that is not strictly speaking blocking it.
|
* Given the choice, we needlessly block a normal grace period rather than
|
* blocking an expedited grace period.
|
*
|
* Note that an endless sequence of expedited grace periods still cannot
|
* indefinitely postpone a normal grace period. Eventually, all of the
|
* fixed number of preempted tasks blocking the normal grace period that are
|
* not also blocking the expedited grace period will resume and complete
|
* their RCU read-side critical sections. At that point, the ->gp_tasks
|
* pointer will equal the ->exp_tasks pointer, at which point the end of
|
* the corresponding expedited grace period will also be the end of the
|
* normal grace period.
|
*/
|
static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
|
__releases(rnp->lock) /* But leaves rrupts disabled. */
|
{
|
int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
|
(rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
|
(rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
|
(rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
|
struct task_struct *t = current;
|
|
raw_lockdep_assert_held_rcu_node(rnp);
|
WARN_ON_ONCE(rdp->mynode != rnp);
|
WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
|
/* RCU better not be waiting on newly onlined CPUs! */
|
WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
|
rdp->grpmask);
|
|
/*
|
* Decide where to queue the newly blocked task. In theory,
|
* this could be an if-statement. In practice, when I tried
|
* that, it was quite messy.
|
*/
|
switch (blkd_state) {
|
case 0:
|
case RCU_EXP_TASKS:
|
case RCU_EXP_TASKS + RCU_GP_BLKD:
|
case RCU_GP_TASKS:
|
case RCU_GP_TASKS + RCU_EXP_TASKS:
|
|
/*
|
* Blocking neither GP, or first task blocking the normal
|
* GP but not blocking the already-waiting expedited GP.
|
* Queue at the head of the list to avoid unnecessarily
|
* blocking the already-waiting GPs.
|
*/
|
list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
|
break;
|
|
case RCU_EXP_BLKD:
|
case RCU_GP_BLKD:
|
case RCU_GP_BLKD + RCU_EXP_BLKD:
|
case RCU_GP_TASKS + RCU_EXP_BLKD:
|
case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
|
case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
|
|
/*
|
* First task arriving that blocks either GP, or first task
|
* arriving that blocks the expedited GP (with the normal
|
* GP already waiting), or a task arriving that blocks
|
* both GPs with both GPs already waiting. Queue at the
|
* tail of the list to avoid any GP waiting on any of the
|
* already queued tasks that are not blocking it.
|
*/
|
list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
|
break;
|
|
case RCU_EXP_TASKS + RCU_EXP_BLKD:
|
case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
|
case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
|
|
/*
|
* Second or subsequent task blocking the expedited GP.
|
* The task either does not block the normal GP, or is the
|
* first task blocking the normal GP. Queue just after
|
* the first task blocking the expedited GP.
|
*/
|
list_add(&t->rcu_node_entry, rnp->exp_tasks);
|
break;
|
|
case RCU_GP_TASKS + RCU_GP_BLKD:
|
case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
|
|
/*
|
* Second or subsequent task blocking the normal GP.
|
* The task does not block the expedited GP. Queue just
|
* after the first task blocking the normal GP.
|
*/
|
list_add(&t->rcu_node_entry, rnp->gp_tasks);
|
break;
|
|
default:
|
|
/* Yet another exercise in excessive paranoia. */
|
WARN_ON_ONCE(1);
|
break;
|
}
|
|
/*
|
* We have now queued the task. If it was the first one to
|
* block either grace period, update the ->gp_tasks and/or
|
* ->exp_tasks pointers, respectively, to reference the newly
|
* blocked tasks.
|
*/
|
if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
|
WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);
|
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
|
}
|
if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
|
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) !=
|
!(rnp->expmask & rdp->grpmask));
|
raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
|
|
/*
|
* Report the quiescent state for the expedited GP. This expedited
|
* GP should not be able to end until we report, so there should be
|
* 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 && rdp->exp_deferred_qs)
|
rcu_report_exp_rdp(rdp);
|
else
|
WARN_ON_ONCE(rdp->exp_deferred_qs);
|
}
|
|
/*
|
* Record a preemptible-RCU quiescent state for the specified CPU.
|
* Note that this does not necessarily mean that the task currently running
|
* on the CPU is in a quiescent state: Instead, it means that the current
|
* grace period need not wait on any RCU read-side critical section that
|
* starts later on this CPU. It also means that if the current task is
|
* in an RCU read-side critical section, it has already added itself to
|
* some leaf rcu_node structure's ->blkd_tasks list. In addition to the
|
* current task, there might be any number of other tasks blocked while
|
* in an RCU read-side critical section.
|
*
|
* Callers to this function must disable preemption.
|
*/
|
static void rcu_qs(void)
|
{
|
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.gp_seq),
|
TPS("cpuqs"));
|
__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);
|
}
|
}
|
|
/*
|
* We have entered the scheduler, and the current task might soon be
|
* context-switched away from. If this task is in an RCU read-side
|
* critical section, we will no longer be able to rely on the CPU to
|
* record that fact, so we enqueue the task on the blkd_tasks list.
|
* The task will dequeue itself when it exits the outermost enclosing
|
* RCU read-side critical section. Therefore, the current grace period
|
* cannot be permitted to complete until the blkd_tasks list entries
|
* predating the current grace period drain, in other words, until
|
* rnp->gp_tasks becomes NULL.
|
*
|
* Caller must disable interrupts.
|
*/
|
void rcu_note_context_switch(bool preempt)
|
{
|
struct task_struct *t = current;
|
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 && 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. */
|
rnp = rdp->mynode;
|
raw_spin_lock_rcu_node(rnp);
|
t->rcu_read_unlock_special.b.blocked = true;
|
t->rcu_blocked_node = rnp;
|
|
/*
|
* Verify the CPU's sanity, trace the preemption, and
|
* then queue the task as required based on the states
|
* of any ongoing and expedited grace periods.
|
*/
|
WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
|
WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
|
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 {
|
rcu_preempt_deferred_qs(t);
|
}
|
|
/*
|
* Either we were not in an RCU read-side critical section to
|
* begin with, or we have now recorded that critical section
|
* globally. Either way, we can now note a quiescent state
|
* for this CPU. Again, if we were in an RCU read-side critical
|
* section, and if that critical section was blocking the current
|
* grace period, then the fact that the task has been enqueued
|
* means that we continue to block the current grace period.
|
*/
|
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
|
* for the specified rcu_node structure. If the caller needs a reliable
|
* answer, it must hold the rcu_node's ->lock.
|
*/
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
{
|
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
|
* if we block.
|
*/
|
void __rcu_read_lock(void)
|
{
|
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);
|
|
/*
|
* Preemptible RCU implementation for rcu_read_unlock().
|
* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
|
* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
|
* invoke rcu_read_unlock_special() to clean up after a context switch
|
* in an RCU read-side critical section and other special cases.
|
*/
|
void __rcu_read_unlock(void)
|
{
|
struct task_struct *t = current;
|
|
if (rcu_preempt_read_exit() == 0) {
|
barrier(); /* critical section before exit code. */
|
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
|
rcu_read_unlock_special(t);
|
}
|
if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
|
int rrln = rcu_preempt_depth();
|
|
WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX);
|
}
|
}
|
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
|
|
/*
|
* Advance a ->blkd_tasks-list pointer to the next entry, instead
|
* returning NULL if at the end of the list.
|
*/
|
static struct list_head *rcu_next_node_entry(struct task_struct *t,
|
struct rcu_node *rnp)
|
{
|
struct list_head *np;
|
|
np = t->rcu_node_entry.next;
|
if (np == &rnp->blkd_tasks)
|
np = NULL;
|
return np;
|
}
|
|
/*
|
* Return true if the specified rcu_node structure has tasks that were
|
* preempted within an RCU read-side critical section.
|
*/
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
{
|
return !list_empty(&rnp->blkd_tasks);
|
}
|
|
/*
|
* 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_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
|
{
|
bool empty_exp;
|
bool empty_norm;
|
bool empty_exp_now;
|
struct list_head *np;
|
bool drop_boost_mutex = false;
|
struct rcu_data *rdp;
|
struct rcu_node *rnp;
|
union rcu_special special;
|
|
/*
|
* If RCU core is waiting for this CPU to exit its critical section,
|
* report the fact that it has exited. Because irqs are disabled,
|
* 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) {
|
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
|
rcu_report_qs_rdp(rdp);
|
udelay(rcu_unlock_delay);
|
} else {
|
rcu_qs();
|
}
|
}
|
|
/*
|
* 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 (rdp->exp_deferred_qs)
|
rcu_report_exp_rdp(rdp);
|
|
/* Clean up if blocked during RCU read-side critical section. */
|
if (special.b.blocked) {
|
|
/*
|
* Remove this task from the list it blocked on. The task
|
* now remains queued on the rcu_node corresponding to the
|
* CPU it first blocked on, so there is no longer any need
|
* to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
|
*/
|
rnp = t->rcu_blocked_node;
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
WARN_ON_ONCE(rnp != t->rcu_blocked_node);
|
WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
|
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
|
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
|
(!empty_norm || rnp->qsmask));
|
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);
|
t->rcu_blocked_node = NULL;
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
|
rnp->gp_seq, t->pid);
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
WRITE_ONCE(rnp->gp_tasks, np);
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
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)
|
WRITE_ONCE(rnp->boost_tasks, np);
|
}
|
|
/*
|
* If this was the last task on the current list, and if
|
* we aren't waiting on any CPUs, report the quiescent state.
|
* 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_exp_done(rnp);
|
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
|
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
|
rnp->gp_seq,
|
0, rnp->qsmask,
|
rnp->level,
|
rnp->grplo,
|
rnp->grphi,
|
!!rnp->gp_tasks);
|
rcu_report_unblock_qs_rnp(rnp, flags);
|
} else {
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
}
|
|
/*
|
* 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(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);
|
}
|
}
|
|
/*
|
* 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 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;
|
|
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;
|
}
|
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.
|
*
|
* 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_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(rnp, 10);
|
if (rcu_preempt_has_tasks(rnp) &&
|
(rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
|
WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
|
t = container_of(rnp->gp_tasks, struct task_struct,
|
rcu_node_entry);
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
|
rnp->gp_seq, t->pid);
|
}
|
WARN_ON_ONCE(rnp->qsmask);
|
}
|
|
/*
|
* 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_flavor_sched_clock_irq(int user)
|
{
|
struct task_struct *t = current;
|
|
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 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, rcu_state.gp_start + HZ))
|
t->rcu_read_unlock_special.b.need_qs = true;
|
}
|
|
/*
|
* 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.
|
* 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 (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;
|
}
|
__rcu_read_unlock();
|
rcu_preempt_deferred_qs(current);
|
}
|
|
/*
|
* Dump the blocked-tasks state, but limit the list dump to the
|
* specified number of elements.
|
*/
|
static void
|
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
|
{
|
int cpu;
|
int i;
|
struct list_head *lhp;
|
bool onl;
|
struct rcu_data *rdp;
|
struct rcu_node *rnp1;
|
|
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)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), 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 >= ncheck)
|
break;
|
}
|
pr_cont("\n");
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; 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],
|
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
|
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
|
}
|
}
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */
|
|
/*
|
* 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.
|
*/
|
static void __init rcu_bootup_announce(void)
|
{
|
pr_info("Hierarchical RCU implementation.\n");
|
rcu_bootup_announce_oddness();
|
}
|
|
/*
|
* 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_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
|
* RCU readers.
|
*/
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
{
|
return 0;
|
}
|
|
/*
|
* Because there is no preemptible RCU, there can be no readers blocked.
|
*/
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
{
|
return false;
|
}
|
|
/*
|
* Because there is no preemptible RCU, there can be no deferred quiescent
|
* states.
|
*/
|
static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
|
{
|
return false;
|
}
|
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_node *rnp)
|
{
|
WARN_ON_ONCE(rnp->qsmask);
|
}
|
|
/*
|
* Check to see if this CPU is in a non-context-switch quiescent state,
|
* namely user mode and idle loop.
|
*/
|
static void rcu_flavor_sched_clock_irq(int user)
|
{
|
if (user || rcu_is_cpu_rrupt_from_idle()) {
|
|
/*
|
* 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.
|
*/
|
|
rcu_qs();
|
}
|
}
|
|
/*
|
* Because preemptible RCU does not exist, tasks cannot possibly exit
|
* while in preemptible RCU read-side critical sections.
|
*/
|
void exit_rcu(void)
|
{
|
}
|
|
/*
|
* Dump the guaranteed-empty blocked-tasks state. Trust but verify.
|
*/
|
static void
|
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
|
{
|
WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
|
}
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|
|
/*
|
* If boosting, set rcuc kthreads to realtime priority.
|
*/
|
static void rcu_cpu_kthread_setup(unsigned int cpu)
|
{
|
#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
|
* or ->boost_tasks, advancing the pointer to the next task in the
|
* ->blkd_tasks list.
|
*
|
* Note that irqs must be enabled: boosting the task can block.
|
* Returns 1 if there are more tasks needing to be boosted.
|
*/
|
static int rcu_boost(struct rcu_node *rnp)
|
{
|
unsigned long flags;
|
struct task_struct *t;
|
struct list_head *tb;
|
|
if (READ_ONCE(rnp->exp_tasks) == NULL &&
|
READ_ONCE(rnp->boost_tasks) == NULL)
|
return 0; /* Nothing left to boost. */
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
/*
|
* Recheck under the lock: all tasks in need of boosting
|
* might exit their RCU read-side critical sections on their own.
|
*/
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
return 0;
|
}
|
|
/*
|
* Preferentially boost tasks blocking expedited grace periods.
|
* This cannot starve the normal grace periods because a second
|
* expedited grace period must boost all blocked tasks, including
|
* those blocking the pre-existing normal grace period.
|
*/
|
if (rnp->exp_tasks != NULL)
|
tb = rnp->exp_tasks;
|
else
|
tb = rnp->boost_tasks;
|
|
/*
|
* We boost task t by manufacturing an rt_mutex that appears to
|
* be held by task t. We leave a pointer to that rt_mutex where
|
* task t can find it, and task t will release the mutex when it
|
* exits its outermost RCU read-side critical section. Then
|
* simply acquiring this artificial rt_mutex will boost task
|
* t's priority. (Thanks to tglx for suggesting this approach!)
|
*
|
* Note that task t must acquire rnp->lock to remove itself from
|
* the ->blkd_tasks list, which it will do from exit() if from
|
* nowhere else. We therefore are guaranteed that task t will
|
* stay around at least until we drop rnp->lock. Note that
|
* rnp->lock also resolves races between our priority boosting
|
* and task t's exiting its outermost RCU read-side critical
|
* section.
|
*/
|
t = container_of(tb, struct task_struct, rcu_node_entry);
|
rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
/* Lock only for side effect: boosts task t's priority. */
|
rt_mutex_lock(&rnp->boost_mtx);
|
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
|
|
return READ_ONCE(rnp->exp_tasks) != NULL ||
|
READ_ONCE(rnp->boost_tasks) != NULL;
|
}
|
|
/*
|
* Priority-boosting kthread, one per leaf rcu_node.
|
*/
|
static int rcu_boost_kthread(void *arg)
|
{
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
int spincnt = 0;
|
int more2boost;
|
|
trace_rcu_utilization(TPS("Start boost kthread@init"));
|
for (;;) {
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
|
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
|
rcu_wait(READ_ONCE(rnp->boost_tasks) ||
|
READ_ONCE(rnp->exp_tasks));
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
|
more2boost = rcu_boost(rnp);
|
if (more2boost)
|
spincnt++;
|
else
|
spincnt = 0;
|
if (spincnt > 10) {
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);
|
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
|
schedule_timeout_idle(2);
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
|
spincnt = 0;
|
}
|
}
|
/* NOTREACHED */
|
trace_rcu_utilization(TPS("End boost kthread@notreached"));
|
return 0;
|
}
|
|
/*
|
* Check to see if it is time to start boosting RCU readers that are
|
* blocking the current grace period, and, if so, tell the per-rcu_node
|
* kthread to start boosting them. If there is an expedited grace
|
* period in progress, it is always time to boost.
|
*
|
* The caller must hold rnp->lock, which this function releases.
|
* The ->boost_kthread_task is immortal, so we don't need to worry
|
* about it going away.
|
*/
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
__releases(rnp->lock)
|
{
|
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);
|
return;
|
}
|
if (rnp->exp_tasks != NULL ||
|
(rnp->gp_tasks != NULL &&
|
rnp->boost_tasks == NULL &&
|
rnp->qsmask == 0 &&
|
(!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) {
|
if (rnp->exp_tasks == NULL)
|
WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
rcu_wake_cond(rnp->boost_kthread_task,
|
READ_ONCE(rnp->boost_kthread_status));
|
} else {
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
}
|
}
|
|
/*
|
* Is the current CPU running the RCU-callbacks kthread?
|
* Caller must have preemption disabled.
|
*/
|
static bool rcu_is_callbacks_kthread(void)
|
{
|
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)
|
|
/*
|
* Do priority-boost accounting for the start of a new grace period.
|
*/
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
{
|
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
|
}
|
|
/*
|
* Create an RCU-boost kthread for the specified node if one does not
|
* already exist. We only create this kthread for preemptible RCU.
|
* Returns zero if all is well, a negated errno otherwise.
|
*/
|
static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
|
{
|
int rnp_index = rnp - rcu_get_root();
|
unsigned long flags;
|
struct sched_param sp;
|
struct task_struct *t;
|
|
if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
|
return;
|
|
if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
|
return;
|
|
rcu_state.boost = 1;
|
|
if (rnp->boost_kthread_task != NULL)
|
return;
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
"rcub/%d", rnp_index);
|
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. */
|
}
|
|
/*
|
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
* served by the rcu_node in question. The CPU hotplug lock is still
|
* held, so the value of rnp->qsmaskinit will be stable.
|
*
|
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
* this function allows the kthread to execute on any CPU.
|
*/
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
{
|
struct task_struct *t = rnp->boost_kthread_task;
|
unsigned long mask = rcu_rnp_online_cpus(rnp);
|
cpumask_var_t cm;
|
int cpu;
|
|
if (!t)
|
return;
|
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
return;
|
for_each_leaf_node_possible_cpu(rnp, cpu)
|
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
|
cpu != outgoingcpu)
|
cpumask_set_cpu(cpu, cm);
|
if (cpumask_weight(cm) == 0)
|
cpumask_setall(cm);
|
set_cpus_allowed_ptr(t, cm);
|
free_cpumask_var(cm);
|
}
|
|
/*
|
* Spawn boost kthreads -- called as soon as the scheduler is running.
|
*/
|
static void __init rcu_spawn_boost_kthreads(void)
|
{
|
struct rcu_node *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_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)
|
rcu_spawn_one_boost_kthread(rnp);
|
}
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
__releases(rnp->lock)
|
{
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
}
|
|
static bool rcu_is_callbacks_kthread(void)
|
{
|
return false;
|
}
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
{
|
}
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
{
|
}
|
|
static void __init rcu_spawn_boost_kthreads(void)
|
{
|
}
|
|
static void rcu_prepare_kthreads(int cpu)
|
{
|
}
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
#if !defined(CONFIG_RCU_FAST_NO_HZ)
|
|
/*
|
* 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 or not this
|
* CPU has RCU callbacks queued.
|
*/
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
{
|
*nextevt = KTIME_MAX;
|
return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
|
!rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
|
}
|
|
/*
|
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
|
* after it.
|
*/
|
static void rcu_cleanup_after_idle(void)
|
{
|
}
|
|
/*
|
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
|
* is nothing.
|
*/
|
static void rcu_prepare_for_idle(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.
|
*
|
* 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
|
* is sized to be roughly one RCU grace period. Those energy-efficiency
|
* benchmarkers who might otherwise be tempted to set this to a large
|
* 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!
|
*
|
* 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. */
|
|
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
|
module_param(rcu_idle_gp_delay, int, 0644);
|
|
/*
|
* 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 = this_cpu_ptr(&rcu_data);
|
struct rcu_node *rnp;
|
|
/* Exit early if we advanced recently. */
|
if (jiffies == rdp->last_advance_all)
|
return false;
|
rdp->last_advance_all = jiffies;
|
|
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(rdp);
|
|
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 about what to set the timeout.
|
*
|
* The caller must have disabled interrupts.
|
*/
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
{
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
unsigned long dj;
|
|
lockdep_assert_irqs_disabled();
|
|
/* 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;
|
}
|
|
/* Attempt to advance callbacks. */
|
if (rcu_try_advance_all_cbs()) {
|
/* Some ready to invoke, so initiate later invocation. */
|
invoke_rcu_core();
|
return 1;
|
}
|
rdp->last_accelerate = 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 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 = this_cpu_ptr(&rcu_data);
|
struct rcu_node *rnp;
|
int tne;
|
|
lockdep_assert_irqs_disabled();
|
if (rcu_segcblist_is_offloaded(&rdp->cblist))
|
return;
|
|
/* Handle nohz enablement switches conservatively. */
|
tne = READ_ONCE(tick_nohz_active);
|
if (tne != rdp->tick_nohz_enabled_snap) {
|
if (!rcu_segcblist_empty(&rdp->cblist))
|
invoke_rcu_core(); /* force nohz to see update. */
|
rdp->tick_nohz_enabled_snap = tne;
|
return;
|
}
|
if (!tne)
|
return;
|
|
/*
|
* If we have not yet accelerated this jiffy, accelerate all
|
* callbacks on this CPU.
|
*/
|
if (rdp->last_accelerate == jiffies)
|
return;
|
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(rnp, rdp);
|
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
if (needwake)
|
rcu_gp_kthread_wake();
|
}
|
}
|
|
/*
|
* Clean up for exit from idle. Attempt to advance callbacks based on
|
* any grace periods that elapsed while the CPU was idle, and if any
|
* callbacks are now ready to invoke, initiate invocation.
|
*/
|
static void rcu_cleanup_after_idle(void)
|
{
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
lockdep_assert_irqs_disabled();
|
if (rcu_segcblist_is_offloaded(&rdp->cblist))
|
return;
|
if (rcu_try_advance_all_cbs())
|
invoke_rcu_core();
|
}
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
/*
|
* Offload callback processing from the boot-time-specified set of CPUs
|
* 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 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.
|
* 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);
|
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);
|
|
static int __init parse_rcu_nocb_poll(char *arg)
|
{
|
rcu_nocb_poll = true;
|
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
|
* grace period.
|
*/
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
{
|
swake_up_all(sq);
|
}
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
{
|
return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
|
}
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
{
|
init_swait_queue_head(&rnp->nocb_gp_wq[0]);
|
init_swait_queue_head(&rnp->nocb_gp_wq[1]);
|
}
|
|
/* Is the specified CPU a no-CBs CPU? */
|
bool rcu_is_nocb_cpu(int cpu)
|
{
|
if (cpumask_available(rcu_nocb_mask))
|
return cpumask_test_cpu(cpu, rcu_nocb_mask);
|
return false;
|
}
|
|
/*
|
* Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
|
* and this function releases it.
|
*/
|
static void wake_nocb_gp(struct rcu_data *rdp, bool force,
|
unsigned long flags)
|
__releases(rdp->nocb_lock)
|
{
|
bool needwake = false;
|
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
|
|
lockdep_assert_held(&rdp->nocb_lock);
|
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 (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);
|
}
|
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);
|
}
|
|
/*
|
* 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_gp_defer(struct rcu_data *rdp, int waketype,
|
const char *reason)
|
{
|
if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
|
mod_timer(&rdp->nocb_timer, jiffies + 1);
|
if (rdp->nocb_defer_wakeup < waketype)
|
WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
|
}
|
|
/*
|
* 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_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
unsigned long j)
|
{
|
struct rcu_cblist rcl;
|
|
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;
|
}
|
/* 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;
|
}
|
|
/*
|
* 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_wake(struct rcu_data *rdp, bool was_alldone,
|
unsigned long flags)
|
__releases(rdp->nocb_lock)
|
{
|
unsigned long cur_gp_seq;
|
unsigned long j;
|
long len;
|
struct task_struct *t;
|
|
// 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(rcu_state.name, rdp->cpu,
|
TPS("WakeNotPoll"));
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
return;
|
}
|
// 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_gp(rdp, false, flags);
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
TPS("WakeEmpty"));
|
} else {
|
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
|
TPS("WakeEmptyIsDeferred"));
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
}
|
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
|
/* ... or if many callbacks queued. */
|
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;
|
}
|
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(rcu_state.name, rdp->cpu, TPS("WakeNot"));
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
}
|
return;
|
}
|
|
/* 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);
|
|
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;
|
|
/*
|
* 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.
|
*/
|
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();
|
}
|
|
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));
|
}
|
|
/*
|
* 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 int rcu_nocb_gp_kthread(void *arg)
|
{
|
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;
|
}
|
|
/*
|
* Invoke any ready callbacks from the corresponding no-CBs CPU,
|
* then, if there are no more, wait for more to appear.
|
*/
|
static void nocb_cb_wait(struct rcu_data *rdp)
|
{
|
unsigned long cur_gp_seq;
|
unsigned long flags;
|
bool needwake_gp = false;
|
struct rcu_node *rnp = rdp->mynode;
|
|
local_irq_save(flags);
|
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;
|
}
|
|
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;
|
}
|
WARN_ON(signal_pending(current));
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
|
}
|
|
/*
|
* Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
|
* nocb_cb_wait() to do the dirty work.
|
*/
|
static int rcu_nocb_cb_kthread(void *arg)
|
{
|
struct rcu_data *rdp = arg;
|
|
// Each pass through this loop does one callback batch, and,
|
// if there are no more ready callbacks, waits for them.
|
for (;;) {
|
nocb_cb_wait(rdp);
|
cond_resched_tasks_rcu_qs();
|
}
|
return 0;
|
}
|
|
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
|
{
|
return READ_ONCE(rdp->nocb_defer_wakeup);
|
}
|
|
/* Do a deferred wakeup of rcu_nocb_kthread(). */
|
static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
|
{
|
unsigned long flags;
|
int ndw;
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
if (!rcu_nocb_need_deferred_wakeup(rdp)) {
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
return;
|
}
|
ndw = READ_ONCE(rdp->nocb_defer_wakeup);
|
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. */
|
static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
|
{
|
struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
|
|
do_nocb_deferred_wakeup_common(rdp);
|
}
|
|
/*
|
* Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
|
* This means we do an inexact common-case check. Note that if
|
* we miss, ->nocb_timer will eventually clean things up.
|
*/
|
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
{
|
if (rcu_nocb_need_deferred_wakeup(rdp))
|
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_data *rdp;
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
|
need_rcu_nocb_mask = true;
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
|
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
|
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
|
return;
|
}
|
}
|
if (!cpumask_available(rcu_nocb_mask))
|
return;
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
if (tick_nohz_full_running)
|
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
|
pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
|
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
|
rcu_nocb_mask);
|
}
|
if (cpumask_empty(rcu_nocb_mask))
|
pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
|
else
|
pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
|
cpumask_pr_args(rcu_nocb_mask));
|
if (rcu_nocb_poll)
|
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
|
|
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)
|
{
|
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 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(int 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->nocb_cb_kthread)
|
return;
|
|
/* 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. */
|
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 kthread, spawn it.
|
*/
|
static void rcu_spawn_cpu_nocb_kthread(int cpu)
|
{
|
if (rcu_scheduler_fully_active)
|
rcu_spawn_one_nocb_kthread(cpu);
|
}
|
|
/*
|
* Once the scheduler is running, spawn rcuo kthreads for all online
|
* no-CBs CPUs. This assumes that the early_initcall()s happen before
|
* non-boot CPUs come online -- if this changes, we will need to add
|
* some mutual exclusion.
|
*/
|
static void __init rcu_spawn_nocb_kthreads(void)
|
{
|
int cpu;
|
|
for_each_online_cpu(cpu)
|
rcu_spawn_cpu_nocb_kthread(cpu);
|
}
|
|
/* 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 GP-CB relationships for all no-CBs CPU.
|
*/
|
static void __init rcu_organize_nocb_kthreads(void)
|
{
|
int cpu;
|
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_gp = NULL; /* Suppress misguided gcc warn. */
|
struct rcu_data *rdp_prev = NULL;
|
|
if (!cpumask_available(rcu_nocb_mask))
|
return;
|
if (ls == -1) {
|
ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
|
rcu_nocb_gp_stride = ls;
|
}
|
|
/*
|
* Each pass through this loop sets up one rcu_data structure.
|
* Should the corresponding CPU come online in the future, then
|
* we will spawn the needed set of rcu_nocb_kthread() kthreads.
|
*/
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
if (rdp->cpu >= nl) {
|
/* New GP kthread, set up for CBs & next GP. */
|
gotnocbs = true;
|
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
|
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 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)");
|
}
|
|
/*
|
* 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 (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);
|
|
/*
|
* 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 */
|
|
/* No ->nocb_lock to acquire. */
|
static void rcu_nocb_lock(struct rcu_data *rdp)
|
{
|
}
|
|
/* 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)
|
{
|
}
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
{
|
return NULL;
|
}
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
{
|
}
|
|
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 void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
|
unsigned long flags)
|
{
|
WARN_ON_ONCE(1); /* Should be dead code! */
|
}
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
{
|
}
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
|
{
|
return false;
|
}
|
|
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
{
|
}
|
|
static void rcu_spawn_cpu_nocb_kthread(int cpu)
|
{
|
}
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
{
|
}
|
|
static void show_rcu_nocb_state(struct rcu_data *rdp)
|
{
|
}
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|
|
/*
|
* Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
|
* grace-period kthread will do force_quiescent_state() processing?
|
* The idea is to avoid waking up RCU core processing on such a
|
* CPU unless the grace period has extended for too long.
|
*
|
* 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(void)
|
{
|
#ifdef CONFIG_NO_HZ_FULL
|
if (tick_nohz_full_cpu(smp_processor_id()) &&
|
(!rcu_gp_in_progress() ||
|
time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
|
return true;
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
return false;
|
}
|
|
/*
|
* Bind the RCU grace-period kthreads to the housekeeping CPU.
|
*/
|
static void rcu_bind_gp_kthread(void)
|
{
|
if (!tick_nohz_full_enabled())
|
return;
|
housekeeping_affine(current, HK_FLAG_RCU);
|
}
|
|
/* Record the current task on dyntick-idle entry. */
|
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());
|
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
|
}
|
|
/* Record no current task on dyntick-idle exit. */
|
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 */
|
}
|
