// SPDX-License-Identifier: GPL-2.0+
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/*
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* Sleepable Read-Copy Update mechanism for mutual exclusion.
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*
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* Copyright (C) IBM Corporation, 2006
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* Copyright (C) Fujitsu, 2012
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*
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* Authors: Paul McKenney <paulmck@linux.ibm.com>
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* Lai Jiangshan <laijs@cn.fujitsu.com>
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU/ *.txt
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*
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*/
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#define pr_fmt(fmt) "rcu: " fmt
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#include <linux/export.h>
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#include <linux/mutex.h>
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#include <linux/percpu.h>
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#include <linux/preempt.h>
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#include <linux/rcupdate_wait.h>
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#include <linux/sched.h>
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#include <linux/smp.h>
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#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/srcu.h>
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#include "rcu.h"
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#include "rcu_segcblist.h"
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/* Holdoff in nanoseconds for auto-expediting. */
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#define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
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static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
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module_param(exp_holdoff, ulong, 0444);
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/* Overflow-check frequency. N bits roughly says every 2**N grace periods. */
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static ulong counter_wrap_check = (ULONG_MAX >> 2);
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module_param(counter_wrap_check, ulong, 0444);
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/* Early-boot callback-management, so early that no lock is required! */
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static LIST_HEAD(srcu_boot_list);
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static bool __read_mostly srcu_init_done;
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static void srcu_invoke_callbacks(struct work_struct *work);
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static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay);
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static void process_srcu(struct work_struct *work);
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static void srcu_delay_timer(struct timer_list *t);
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/* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */
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#define spin_lock_rcu_node(p) \
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do { \
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spin_lock(&ACCESS_PRIVATE(p, lock)); \
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smp_mb__after_unlock_lock(); \
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} while (0)
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#define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock))
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#define spin_lock_irq_rcu_node(p) \
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do { \
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spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \
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smp_mb__after_unlock_lock(); \
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} while (0)
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#define spin_unlock_irq_rcu_node(p) \
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spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
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#define spin_lock_irqsave_rcu_node(p, flags) \
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do { \
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spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \
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smp_mb__after_unlock_lock(); \
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} while (0)
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#define spin_unlock_irqrestore_rcu_node(p, flags) \
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spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \
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/*
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* Initialize SRCU combining tree. Note that statically allocated
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* srcu_struct structures might already have srcu_read_lock() and
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* srcu_read_unlock() running against them. So if the is_static parameter
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* is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
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*/
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static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
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{
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int cpu;
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int i;
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int level = 0;
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int levelspread[RCU_NUM_LVLS];
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struct srcu_data *sdp;
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struct srcu_node *snp;
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struct srcu_node *snp_first;
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/* Initialize geometry if it has not already been initialized. */
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rcu_init_geometry();
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/* Work out the overall tree geometry. */
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ssp->level[0] = &ssp->node[0];
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for (i = 1; i < rcu_num_lvls; i++)
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ssp->level[i] = ssp->level[i - 1] + num_rcu_lvl[i - 1];
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rcu_init_levelspread(levelspread, num_rcu_lvl);
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/* Each pass through this loop initializes one srcu_node structure. */
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srcu_for_each_node_breadth_first(ssp, snp) {
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spin_lock_init(&ACCESS_PRIVATE(snp, lock));
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WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=
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ARRAY_SIZE(snp->srcu_data_have_cbs));
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for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
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snp->srcu_have_cbs[i] = 0;
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snp->srcu_data_have_cbs[i] = 0;
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}
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snp->srcu_gp_seq_needed_exp = 0;
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snp->grplo = -1;
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snp->grphi = -1;
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if (snp == &ssp->node[0]) {
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/* Root node, special case. */
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snp->srcu_parent = NULL;
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continue;
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}
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/* Non-root node. */
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if (snp == ssp->level[level + 1])
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level++;
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snp->srcu_parent = ssp->level[level - 1] +
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(snp - ssp->level[level]) /
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levelspread[level - 1];
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}
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/*
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* Initialize the per-CPU srcu_data array, which feeds into the
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* leaves of the srcu_node tree.
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*/
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WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
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ARRAY_SIZE(sdp->srcu_unlock_count));
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level = rcu_num_lvls - 1;
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snp_first = ssp->level[level];
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for_each_possible_cpu(cpu) {
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sdp = per_cpu_ptr(ssp->sda, cpu);
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spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
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rcu_segcblist_init(&sdp->srcu_cblist);
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sdp->srcu_cblist_invoking = false;
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sdp->srcu_gp_seq_needed = ssp->srcu_gp_seq;
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sdp->srcu_gp_seq_needed_exp = ssp->srcu_gp_seq;
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sdp->mynode = &snp_first[cpu / levelspread[level]];
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for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
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if (snp->grplo < 0)
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snp->grplo = cpu;
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snp->grphi = cpu;
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}
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sdp->cpu = cpu;
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INIT_WORK(&sdp->work, srcu_invoke_callbacks);
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timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
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sdp->ssp = ssp;
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sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
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if (is_static)
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continue;
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/* Dynamically allocated, better be no srcu_read_locks()! */
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for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
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sdp->srcu_lock_count[i] = 0;
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sdp->srcu_unlock_count[i] = 0;
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}
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}
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}
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/*
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* Initialize non-compile-time initialized fields, including the
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* associated srcu_node and srcu_data structures. The is_static
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* parameter is passed through to init_srcu_struct_nodes(), and
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* also tells us that ->sda has already been wired up to srcu_data.
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*/
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static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
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{
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mutex_init(&ssp->srcu_cb_mutex);
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mutex_init(&ssp->srcu_gp_mutex);
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ssp->srcu_idx = 0;
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ssp->srcu_gp_seq = 0;
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ssp->srcu_barrier_seq = 0;
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mutex_init(&ssp->srcu_barrier_mutex);
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atomic_set(&ssp->srcu_barrier_cpu_cnt, 0);
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INIT_DELAYED_WORK(&ssp->work, process_srcu);
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if (!is_static)
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ssp->sda = alloc_percpu(struct srcu_data);
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init_srcu_struct_nodes(ssp, is_static);
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ssp->srcu_gp_seq_needed_exp = 0;
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ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
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smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */
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return ssp->sda ? 0 : -ENOMEM;
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}
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
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struct lock_class_key *key)
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{
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/* Don't re-initialize a lock while it is held. */
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debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
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lockdep_init_map(&ssp->dep_map, name, key, 0);
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spin_lock_init(&ACCESS_PRIVATE(ssp, lock));
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return init_srcu_struct_fields(ssp, false);
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}
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EXPORT_SYMBOL_GPL(__init_srcu_struct);
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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/**
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* init_srcu_struct - initialize a sleep-RCU structure
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* @ssp: structure to initialize.
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*
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* Must invoke this on a given srcu_struct before passing that srcu_struct
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* to any other function. Each srcu_struct represents a separate domain
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* of SRCU protection.
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*/
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int init_srcu_struct(struct srcu_struct *ssp)
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{
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spin_lock_init(&ACCESS_PRIVATE(ssp, lock));
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return init_srcu_struct_fields(ssp, false);
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}
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EXPORT_SYMBOL_GPL(init_srcu_struct);
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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/*
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* First-use initialization of statically allocated srcu_struct
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* structure. Wiring up the combining tree is more than can be
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* done with compile-time initialization, so this check is added
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* to each update-side SRCU primitive. Use ssp->lock, which -is-
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* compile-time initialized, to resolve races involving multiple
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* CPUs trying to garner first-use privileges.
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*/
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static void check_init_srcu_struct(struct srcu_struct *ssp)
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{
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unsigned long flags;
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/* The smp_load_acquire() pairs with the smp_store_release(). */
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if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq_needed))) /*^^^*/
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return; /* Already initialized. */
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spin_lock_irqsave_rcu_node(ssp, flags);
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if (!rcu_seq_state(ssp->srcu_gp_seq_needed)) {
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spin_unlock_irqrestore_rcu_node(ssp, flags);
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return;
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}
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init_srcu_struct_fields(ssp, true);
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spin_unlock_irqrestore_rcu_node(ssp, flags);
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}
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/*
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* Returns approximate total of the readers' ->srcu_lock_count[] values
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* for the rank of per-CPU counters specified by idx.
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*/
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static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx)
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{
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int cpu;
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unsigned long sum = 0;
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for_each_possible_cpu(cpu) {
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struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
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sum += READ_ONCE(cpuc->srcu_lock_count[idx]);
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}
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return sum;
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}
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/*
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* Returns approximate total of the readers' ->srcu_unlock_count[] values
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* for the rank of per-CPU counters specified by idx.
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*/
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static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
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{
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int cpu;
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unsigned long sum = 0;
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for_each_possible_cpu(cpu) {
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struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
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sum += READ_ONCE(cpuc->srcu_unlock_count[idx]);
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}
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return sum;
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}
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/*
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* Return true if the number of pre-existing readers is determined to
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* be zero.
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*/
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static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx)
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{
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unsigned long unlocks;
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unlocks = srcu_readers_unlock_idx(ssp, idx);
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/*
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* Make sure that a lock is always counted if the corresponding
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* unlock is counted. Needs to be a smp_mb() as the read side may
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* contain a read from a variable that is written to before the
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* synchronize_srcu() in the write side. In this case smp_mb()s
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* A and B act like the store buffering pattern.
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*
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* This smp_mb() also pairs with smp_mb() C to prevent accesses
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* after the synchronize_srcu() from being executed before the
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* grace period ends.
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*/
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smp_mb(); /* A */
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/*
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* If the locks are the same as the unlocks, then there must have
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* been no readers on this index at some time in between. This does
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* not mean that there are no more readers, as one could have read
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* the current index but not have incremented the lock counter yet.
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*
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* So suppose that the updater is preempted here for so long
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* that more than ULONG_MAX non-nested readers come and go in
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* the meantime. It turns out that this cannot result in overflow
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* because if a reader modifies its unlock count after we read it
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* above, then that reader's next load of ->srcu_idx is guaranteed
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* to get the new value, which will cause it to operate on the
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* other bank of counters, where it cannot contribute to the
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* overflow of these counters. This means that there is a maximum
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* of 2*NR_CPUS increments, which cannot overflow given current
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* systems, especially not on 64-bit systems.
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*
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* OK, how about nesting? This does impose a limit on nesting
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* of floor(ULONG_MAX/NR_CPUS/2), which should be sufficient,
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* especially on 64-bit systems.
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*/
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return srcu_readers_lock_idx(ssp, idx) == unlocks;
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}
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/**
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* srcu_readers_active - returns true if there are readers. and false
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* otherwise
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* @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
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*
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* Note that this is not an atomic primitive, and can therefore suffer
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* severe errors when invoked on an active srcu_struct. That said, it
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* can be useful as an error check at cleanup time.
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*/
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static bool srcu_readers_active(struct srcu_struct *ssp)
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{
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int cpu;
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unsigned long sum = 0;
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for_each_possible_cpu(cpu) {
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struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
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sum += READ_ONCE(cpuc->srcu_lock_count[0]);
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sum += READ_ONCE(cpuc->srcu_lock_count[1]);
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sum -= READ_ONCE(cpuc->srcu_unlock_count[0]);
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sum -= READ_ONCE(cpuc->srcu_unlock_count[1]);
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}
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return sum;
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}
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#define SRCU_INTERVAL 1
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/*
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* Return grace-period delay, zero if there are expedited grace
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* periods pending, SRCU_INTERVAL otherwise.
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*/
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static unsigned long srcu_get_delay(struct srcu_struct *ssp)
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{
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if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq),
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READ_ONCE(ssp->srcu_gp_seq_needed_exp)))
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return 0;
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return SRCU_INTERVAL;
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}
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/**
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* cleanup_srcu_struct - deconstruct a sleep-RCU structure
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* @ssp: structure to clean up.
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*
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* Must invoke this after you are finished using a given srcu_struct that
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* was initialized via init_srcu_struct(), else you leak memory.
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*/
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void cleanup_srcu_struct(struct srcu_struct *ssp)
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{
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int cpu;
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if (WARN_ON(!srcu_get_delay(ssp)))
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return; /* Just leak it! */
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if (WARN_ON(srcu_readers_active(ssp)))
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return; /* Just leak it! */
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flush_delayed_work(&ssp->work);
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for_each_possible_cpu(cpu) {
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struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
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del_timer_sync(&sdp->delay_work);
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flush_work(&sdp->work);
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if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist)))
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return; /* Forgot srcu_barrier(), so just leak it! */
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}
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if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
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WARN_ON(srcu_readers_active(ssp))) {
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pr_info("%s: Active srcu_struct %p state: %d\n",
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__func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)));
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return; /* Caller forgot to stop doing call_srcu()? */
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}
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free_percpu(ssp->sda);
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ssp->sda = NULL;
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}
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EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
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/*
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* Counts the new reader in the appropriate per-CPU element of the
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* srcu_struct.
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* Returns an index that must be passed to the matching srcu_read_unlock().
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*/
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int __srcu_read_lock(struct srcu_struct *ssp)
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{
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int idx;
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idx = READ_ONCE(ssp->srcu_idx) & 0x1;
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this_cpu_inc(ssp->sda->srcu_lock_count[idx]);
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smp_mb(); /* B */ /* Avoid leaking the critical section. */
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return idx;
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}
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EXPORT_SYMBOL_GPL(__srcu_read_lock);
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/*
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* Removes the count for the old reader from the appropriate per-CPU
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* element of the srcu_struct. Note that this may well be a different
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* CPU than that which was incremented by the corresponding srcu_read_lock().
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*/
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void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
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{
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smp_mb(); /* C */ /* Avoid leaking the critical section. */
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this_cpu_inc(ssp->sda->srcu_unlock_count[idx]);
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}
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EXPORT_SYMBOL_GPL(__srcu_read_unlock);
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/*
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* We use an adaptive strategy for synchronize_srcu() and especially for
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* synchronize_srcu_expedited(). We spin for a fixed time period
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* (defined below) to allow SRCU readers to exit their read-side critical
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* sections. If there are still some readers after a few microseconds,
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* we repeatedly block for 1-millisecond time periods.
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*/
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#define SRCU_RETRY_CHECK_DELAY 5
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/*
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* Start an SRCU grace period.
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*/
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static void srcu_gp_start(struct srcu_struct *ssp)
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{
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struct srcu_data *sdp = this_cpu_ptr(ssp->sda);
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int state;
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lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock));
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WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
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spin_lock_rcu_node(sdp); /* Interrupts already disabled. */
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rcu_segcblist_advance(&sdp->srcu_cblist,
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rcu_seq_current(&ssp->srcu_gp_seq));
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(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
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rcu_seq_snap(&ssp->srcu_gp_seq));
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spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */
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smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
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rcu_seq_start(&ssp->srcu_gp_seq);
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state = rcu_seq_state(ssp->srcu_gp_seq);
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WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
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}
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|
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static void srcu_delay_timer(struct timer_list *t)
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{
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struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work);
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queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
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}
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static void srcu_queue_delayed_work_on(struct srcu_data *sdp,
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unsigned long delay)
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{
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if (!delay) {
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queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
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return;
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}
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timer_reduce(&sdp->delay_work, jiffies + delay);
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}
|
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/*
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* Schedule callback invocation for the specified srcu_data structure,
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* if possible, on the corresponding CPU.
|
*/
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static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
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{
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srcu_queue_delayed_work_on(sdp, delay);
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}
|
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/*
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* Schedule callback invocation for all srcu_data structures associated
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* with the specified srcu_node structure that have callbacks for the
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* just-completed grace period, the one corresponding to idx. If possible,
|
* schedule this invocation on the corresponding CPUs.
|
*/
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static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp,
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unsigned long mask, unsigned long delay)
|
{
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int cpu;
|
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for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
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if (!(mask & (1 << (cpu - snp->grplo))))
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continue;
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srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
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}
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}
|
|
/*
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* Note the end of an SRCU grace period. Initiates callback invocation
|
* and starts a new grace period if needed.
|
*
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* The ->srcu_cb_mutex acquisition does not protect any data, but
|
* instead prevents more than one grace period from starting while we
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* are initiating callback invocation. This allows the ->srcu_have_cbs[]
|
* array to have a finite number of elements.
|
*/
|
static void srcu_gp_end(struct srcu_struct *ssp)
|
{
|
unsigned long cbdelay;
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bool cbs;
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bool last_lvl;
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int cpu;
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unsigned long flags;
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unsigned long gpseq;
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int idx;
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unsigned long mask;
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struct srcu_data *sdp;
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struct srcu_node *snp;
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/* Prevent more than one additional grace period. */
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mutex_lock(&ssp->srcu_cb_mutex);
|
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/* End the current grace period. */
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spin_lock_irq_rcu_node(ssp);
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idx = rcu_seq_state(ssp->srcu_gp_seq);
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WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
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cbdelay = srcu_get_delay(ssp);
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WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns());
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rcu_seq_end(&ssp->srcu_gp_seq);
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gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
|
if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq))
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WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, gpseq);
|
spin_unlock_irq_rcu_node(ssp);
|
mutex_unlock(&ssp->srcu_gp_mutex);
|
/* A new grace period can start at this point. But only one. */
|
|
/* Initiate callback invocation as needed. */
|
idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
|
srcu_for_each_node_breadth_first(ssp, snp) {
|
spin_lock_irq_rcu_node(snp);
|
cbs = false;
|
last_lvl = snp >= ssp->level[rcu_num_lvls - 1];
|
if (last_lvl)
|
cbs = snp->srcu_have_cbs[idx] == gpseq;
|
snp->srcu_have_cbs[idx] = gpseq;
|
rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
|
if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq))
|
WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
|
mask = snp->srcu_data_have_cbs[idx];
|
snp->srcu_data_have_cbs[idx] = 0;
|
spin_unlock_irq_rcu_node(snp);
|
if (cbs)
|
srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay);
|
|
/* Occasionally prevent srcu_data counter wrap. */
|
if (!(gpseq & counter_wrap_check) && last_lvl)
|
for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
|
sdp = per_cpu_ptr(ssp->sda, cpu);
|
spin_lock_irqsave_rcu_node(sdp, flags);
|
if (ULONG_CMP_GE(gpseq,
|
sdp->srcu_gp_seq_needed + 100))
|
sdp->srcu_gp_seq_needed = gpseq;
|
if (ULONG_CMP_GE(gpseq,
|
sdp->srcu_gp_seq_needed_exp + 100))
|
sdp->srcu_gp_seq_needed_exp = gpseq;
|
spin_unlock_irqrestore_rcu_node(sdp, flags);
|
}
|
}
|
|
/* Callback initiation done, allow grace periods after next. */
|
mutex_unlock(&ssp->srcu_cb_mutex);
|
|
/* Start a new grace period if needed. */
|
spin_lock_irq_rcu_node(ssp);
|
gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
|
if (!rcu_seq_state(gpseq) &&
|
ULONG_CMP_LT(gpseq, ssp->srcu_gp_seq_needed)) {
|
srcu_gp_start(ssp);
|
spin_unlock_irq_rcu_node(ssp);
|
srcu_reschedule(ssp, 0);
|
} else {
|
spin_unlock_irq_rcu_node(ssp);
|
}
|
}
|
|
/*
|
* Funnel-locking scheme to scalably mediate many concurrent expedited
|
* grace-period requests. This function is invoked for the first known
|
* expedited request for a grace period that has already been requested,
|
* but without expediting. To start a completely new grace period,
|
* whether expedited or not, use srcu_funnel_gp_start() instead.
|
*/
|
static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp,
|
unsigned long s)
|
{
|
unsigned long flags;
|
|
for (; snp != NULL; snp = snp->srcu_parent) {
|
if (rcu_seq_done(&ssp->srcu_gp_seq, s) ||
|
ULONG_CMP_GE(READ_ONCE(snp->srcu_gp_seq_needed_exp), s))
|
return;
|
spin_lock_irqsave_rcu_node(snp, flags);
|
if (ULONG_CMP_GE(snp->srcu_gp_seq_needed_exp, s)) {
|
spin_unlock_irqrestore_rcu_node(snp, flags);
|
return;
|
}
|
WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
|
spin_unlock_irqrestore_rcu_node(snp, flags);
|
}
|
spin_lock_irqsave_rcu_node(ssp, flags);
|
if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
|
WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);
|
spin_unlock_irqrestore_rcu_node(ssp, flags);
|
}
|
|
/*
|
* Funnel-locking scheme to scalably mediate many concurrent grace-period
|
* requests. The winner has to do the work of actually starting grace
|
* period s. Losers must either ensure that their desired grace-period
|
* number is recorded on at least their leaf srcu_node structure, or they
|
* must take steps to invoke their own callbacks.
|
*
|
* Note that this function also does the work of srcu_funnel_exp_start(),
|
* in some cases by directly invoking it.
|
*/
|
static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
|
unsigned long s, bool do_norm)
|
{
|
unsigned long flags;
|
int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
|
struct srcu_node *snp = sdp->mynode;
|
unsigned long snp_seq;
|
|
/* Each pass through the loop does one level of the srcu_node tree. */
|
for (; snp != NULL; snp = snp->srcu_parent) {
|
if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != sdp->mynode)
|
return; /* GP already done and CBs recorded. */
|
spin_lock_irqsave_rcu_node(snp, flags);
|
if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) {
|
snp_seq = snp->srcu_have_cbs[idx];
|
if (snp == sdp->mynode && snp_seq == s)
|
snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
|
spin_unlock_irqrestore_rcu_node(snp, flags);
|
if (snp == sdp->mynode && snp_seq != s) {
|
srcu_schedule_cbs_sdp(sdp, do_norm
|
? SRCU_INTERVAL
|
: 0);
|
return;
|
}
|
if (!do_norm)
|
srcu_funnel_exp_start(ssp, snp, s);
|
return;
|
}
|
snp->srcu_have_cbs[idx] = s;
|
if (snp == sdp->mynode)
|
snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
|
if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))
|
WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
|
spin_unlock_irqrestore_rcu_node(snp, flags);
|
}
|
|
/* Top of tree, must ensure the grace period will be started. */
|
spin_lock_irqsave_rcu_node(ssp, flags);
|
if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed, s)) {
|
/*
|
* Record need for grace period s. Pair with load
|
* acquire setting up for initialization.
|
*/
|
smp_store_release(&ssp->srcu_gp_seq_needed, s); /*^^^*/
|
}
|
if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
|
WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);
|
|
/* If grace period not already done and none in progress, start it. */
|
if (!rcu_seq_done(&ssp->srcu_gp_seq, s) &&
|
rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {
|
WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
|
srcu_gp_start(ssp);
|
if (likely(srcu_init_done))
|
queue_delayed_work(rcu_gp_wq, &ssp->work,
|
srcu_get_delay(ssp));
|
else if (list_empty(&ssp->work.work.entry))
|
list_add(&ssp->work.work.entry, &srcu_boot_list);
|
}
|
spin_unlock_irqrestore_rcu_node(ssp, flags);
|
}
|
|
/*
|
* Wait until all readers counted by array index idx complete, but
|
* loop an additional time if there is an expedited grace period pending.
|
* The caller must ensure that ->srcu_idx is not changed while checking.
|
*/
|
static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount)
|
{
|
for (;;) {
|
if (srcu_readers_active_idx_check(ssp, idx))
|
return true;
|
if (--trycount + !srcu_get_delay(ssp) <= 0)
|
return false;
|
udelay(SRCU_RETRY_CHECK_DELAY);
|
}
|
}
|
|
/*
|
* Increment the ->srcu_idx counter so that future SRCU readers will
|
* use the other rank of the ->srcu_(un)lock_count[] arrays. This allows
|
* us to wait for pre-existing readers in a starvation-free manner.
|
*/
|
static void srcu_flip(struct srcu_struct *ssp)
|
{
|
/*
|
* Ensure that if this updater saw a given reader's increment
|
* from __srcu_read_lock(), that reader was using an old value
|
* of ->srcu_idx. Also ensure that if a given reader sees the
|
* new value of ->srcu_idx, this updater's earlier scans cannot
|
* have seen that reader's increments (which is OK, because this
|
* grace period need not wait on that reader).
|
*/
|
smp_mb(); /* E */ /* Pairs with B and C. */
|
|
WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
|
|
/*
|
* Ensure that if the updater misses an __srcu_read_unlock()
|
* increment, that task's next __srcu_read_lock() will see the
|
* above counter update. Note that both this memory barrier
|
* and the one in srcu_readers_active_idx_check() provide the
|
* guarantee for __srcu_read_lock().
|
*/
|
smp_mb(); /* D */ /* Pairs with C. */
|
}
|
|
/*
|
* If SRCU is likely idle, return true, otherwise return false.
|
*
|
* Note that it is OK for several current from-idle requests for a new
|
* grace period from idle to specify expediting because they will all end
|
* up requesting the same grace period anyhow. So no loss.
|
*
|
* Note also that if any CPU (including the current one) is still invoking
|
* callbacks, this function will nevertheless say "idle". This is not
|
* ideal, but the overhead of checking all CPUs' callback lists is even
|
* less ideal, especially on large systems. Furthermore, the wakeup
|
* can happen before the callback is fully removed, so we have no choice
|
* but to accept this type of error.
|
*
|
* This function is also subject to counter-wrap errors, but let's face
|
* it, if this function was preempted for enough time for the counters
|
* to wrap, it really doesn't matter whether or not we expedite the grace
|
* period. The extra overhead of a needlessly expedited grace period is
|
* negligible when amortized over that time period, and the extra latency
|
* of a needlessly non-expedited grace period is similarly negligible.
|
*/
|
static bool srcu_might_be_idle(struct srcu_struct *ssp)
|
{
|
unsigned long curseq;
|
unsigned long flags;
|
struct srcu_data *sdp;
|
unsigned long t;
|
unsigned long tlast;
|
|
check_init_srcu_struct(ssp);
|
/* If the local srcu_data structure has callbacks, not idle. */
|
sdp = raw_cpu_ptr(ssp->sda);
|
spin_lock_irqsave_rcu_node(sdp, flags);
|
if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
|
spin_unlock_irqrestore_rcu_node(sdp, flags);
|
return false; /* Callbacks already present, so not idle. */
|
}
|
spin_unlock_irqrestore_rcu_node(sdp, flags);
|
|
/*
|
* No local callbacks, so probabalistically probe global state.
|
* Exact information would require acquiring locks, which would
|
* kill scalability, hence the probabalistic nature of the probe.
|
*/
|
|
/* First, see if enough time has passed since the last GP. */
|
t = ktime_get_mono_fast_ns();
|
tlast = READ_ONCE(ssp->srcu_last_gp_end);
|
if (exp_holdoff == 0 ||
|
time_in_range_open(t, tlast, tlast + exp_holdoff))
|
return false; /* Too soon after last GP. */
|
|
/* Next, check for probable idleness. */
|
curseq = rcu_seq_current(&ssp->srcu_gp_seq);
|
smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */
|
if (ULONG_CMP_LT(curseq, READ_ONCE(ssp->srcu_gp_seq_needed)))
|
return false; /* Grace period in progress, so not idle. */
|
smp_mb(); /* Order ->srcu_gp_seq with prior access. */
|
if (curseq != rcu_seq_current(&ssp->srcu_gp_seq))
|
return false; /* GP # changed, so not idle. */
|
return true; /* With reasonable probability, idle! */
|
}
|
|
/*
|
* SRCU callback function to leak a callback.
|
*/
|
static void srcu_leak_callback(struct rcu_head *rhp)
|
{
|
}
|
|
/*
|
* Start an SRCU grace period, and also queue the callback if non-NULL.
|
*/
|
static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
|
struct rcu_head *rhp, bool do_norm)
|
{
|
unsigned long flags;
|
int idx;
|
bool needexp = false;
|
bool needgp = false;
|
unsigned long s;
|
struct srcu_data *sdp;
|
|
check_init_srcu_struct(ssp);
|
idx = srcu_read_lock(ssp);
|
sdp = raw_cpu_ptr(ssp->sda);
|
spin_lock_irqsave_rcu_node(sdp, flags);
|
if (rhp)
|
rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
|
rcu_segcblist_advance(&sdp->srcu_cblist,
|
rcu_seq_current(&ssp->srcu_gp_seq));
|
s = rcu_seq_snap(&ssp->srcu_gp_seq);
|
(void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
|
if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
|
sdp->srcu_gp_seq_needed = s;
|
needgp = true;
|
}
|
if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
|
sdp->srcu_gp_seq_needed_exp = s;
|
needexp = true;
|
}
|
spin_unlock_irqrestore_rcu_node(sdp, flags);
|
if (needgp)
|
srcu_funnel_gp_start(ssp, sdp, s, do_norm);
|
else if (needexp)
|
srcu_funnel_exp_start(ssp, sdp->mynode, s);
|
srcu_read_unlock(ssp, idx);
|
return s;
|
}
|
|
/*
|
* Enqueue an SRCU callback on the srcu_data structure associated with
|
* the current CPU and the specified srcu_struct structure, initiating
|
* grace-period processing if it is not already running.
|
*
|
* Note that all CPUs must agree that the grace period extended beyond
|
* all pre-existing SRCU 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 corresponding SRCU read-side critical section whose beginning
|
* preceded the call to call_srcu(). It also means that each CPU executing
|
* an SRCU read-side critical section that continues beyond the start of
|
* "func()" must have executed a memory barrier after the call_srcu()
|
* but before the beginning of that SRCU 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_srcu() and CPU B invoked the
|
* resulting SRCU 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_srcu() and the invocation of "func()".
|
* This guarantee applies even if CPU A and CPU B are the same CPU (but
|
* again only if the system has more than one CPU).
|
*
|
* Of course, these guarantees apply only for invocations of call_srcu(),
|
* srcu_read_lock(), and srcu_read_unlock() that are all passed the same
|
* srcu_struct structure.
|
*/
|
static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
|
rcu_callback_t func, bool do_norm)
|
{
|
if (debug_rcu_head_queue(rhp)) {
|
/* Probable double call_srcu(), so leak the callback. */
|
WRITE_ONCE(rhp->func, srcu_leak_callback);
|
WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
|
return;
|
}
|
rhp->func = func;
|
(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
|
}
|
|
/**
|
* call_srcu() - Queue a callback for invocation after an SRCU grace period
|
* @ssp: srcu_struct in queue the callback
|
* @rhp: structure to be used for queueing the SRCU callback.
|
* @func: function to be invoked after the SRCU grace period
|
*
|
* The callback function will be invoked some time after a full SRCU
|
* grace period elapses, in other words after all pre-existing SRCU
|
* read-side critical sections have completed. However, the callback
|
* function might well execute concurrently with other SRCU read-side
|
* critical sections that started after call_srcu() was invoked. SRCU
|
* read-side critical sections are delimited by srcu_read_lock() and
|
* srcu_read_unlock(), and may be nested.
|
*
|
* The callback will be invoked from process context, but must nevertheless
|
* be fast and must not block.
|
*/
|
void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
|
rcu_callback_t func)
|
{
|
__call_srcu(ssp, rhp, func, true);
|
}
|
EXPORT_SYMBOL_GPL(call_srcu);
|
|
/*
|
* Helper function for synchronize_srcu() and synchronize_srcu_expedited().
|
*/
|
static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm)
|
{
|
struct rcu_synchronize rcu;
|
|
RCU_LOCKDEP_WARN(lock_is_held(&ssp->dep_map) ||
|
lock_is_held(&rcu_bh_lock_map) ||
|
lock_is_held(&rcu_lock_map) ||
|
lock_is_held(&rcu_sched_lock_map),
|
"Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
|
|
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
|
return;
|
might_sleep();
|
check_init_srcu_struct(ssp);
|
init_completion(&rcu.completion);
|
init_rcu_head_on_stack(&rcu.head);
|
__call_srcu(ssp, &rcu.head, wakeme_after_rcu, do_norm);
|
wait_for_completion(&rcu.completion);
|
destroy_rcu_head_on_stack(&rcu.head);
|
|
/*
|
* Make sure that later code is ordered after the SRCU grace
|
* period. This pairs with the spin_lock_irq_rcu_node()
|
* in srcu_invoke_callbacks(). Unlike Tree RCU, this is needed
|
* because the current CPU might have been totally uninvolved with
|
* (and thus unordered against) that grace period.
|
*/
|
smp_mb();
|
}
|
|
/**
|
* synchronize_srcu_expedited - Brute-force SRCU grace period
|
* @ssp: srcu_struct with which to synchronize.
|
*
|
* Wait for an SRCU grace period to elapse, but be more aggressive about
|
* spinning rather than blocking when waiting.
|
*
|
* Note that synchronize_srcu_expedited() has the same deadlock and
|
* memory-ordering properties as does synchronize_srcu().
|
*/
|
void synchronize_srcu_expedited(struct srcu_struct *ssp)
|
{
|
__synchronize_srcu(ssp, rcu_gp_is_normal());
|
}
|
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
|
|
/**
|
* synchronize_srcu - wait for prior SRCU read-side critical-section completion
|
* @ssp: srcu_struct with which to synchronize.
|
*
|
* Wait for the count to drain to zero of both indexes. To avoid the
|
* possible starvation of synchronize_srcu(), it waits for the count of
|
* the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
|
* and then flip the srcu_idx and wait for the count of the other index.
|
*
|
* Can block; must be called from process context.
|
*
|
* Note that it is illegal to call synchronize_srcu() from the corresponding
|
* SRCU read-side critical section; doing so will result in deadlock.
|
* However, it is perfectly legal to call synchronize_srcu() on one
|
* srcu_struct from some other srcu_struct's read-side critical section,
|
* as long as the resulting graph of srcu_structs is acyclic.
|
*
|
* There are memory-ordering constraints implied by synchronize_srcu().
|
* On systems with more than one CPU, when synchronize_srcu() returns,
|
* each CPU is guaranteed to have executed a full memory barrier since
|
* the end of its last corresponding SRCU read-side critical section
|
* whose beginning preceded the call to synchronize_srcu(). In addition,
|
* each CPU having an SRCU read-side critical section that extends beyond
|
* the return from synchronize_srcu() is guaranteed to have executed a
|
* full memory barrier after the beginning of synchronize_srcu() and before
|
* the beginning of that SRCU 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 synchronize_srcu(), which returned
|
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
|
* to have executed a full memory barrier during the execution of
|
* synchronize_srcu(). This guarantee applies even if CPU A and CPU B
|
* are the same CPU, but again only if the system has more than one CPU.
|
*
|
* Of course, these memory-ordering guarantees apply only when
|
* synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
|
* passed the same srcu_struct structure.
|
*
|
* If SRCU is likely idle, expedite the first request. This semantic
|
* was provided by Classic SRCU, and is relied upon by its users, so TREE
|
* SRCU must also provide it. Note that detecting idleness is heuristic
|
* and subject to both false positives and negatives.
|
*/
|
void synchronize_srcu(struct srcu_struct *ssp)
|
{
|
if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited())
|
synchronize_srcu_expedited(ssp);
|
else
|
__synchronize_srcu(ssp, true);
|
}
|
EXPORT_SYMBOL_GPL(synchronize_srcu);
|
|
/**
|
* get_state_synchronize_srcu - Provide an end-of-grace-period cookie
|
* @ssp: srcu_struct to provide cookie for.
|
*
|
* This function returns a cookie that can be passed to
|
* poll_state_synchronize_srcu(), which will return true if a full grace
|
* period has elapsed in the meantime. It is the caller's responsibility
|
* to make sure that grace period happens, for example, by invoking
|
* call_srcu() after return from get_state_synchronize_srcu().
|
*/
|
unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
|
{
|
// Any prior manipulation of SRCU-protected data must happen
|
// before the load from ->srcu_gp_seq.
|
smp_mb();
|
return rcu_seq_snap(&ssp->srcu_gp_seq);
|
}
|
EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
|
|
/**
|
* start_poll_synchronize_srcu - Provide cookie and start grace period
|
* @ssp: srcu_struct to provide cookie for.
|
*
|
* This function returns a cookie that can be passed to
|
* poll_state_synchronize_srcu(), which will return true if a full grace
|
* period has elapsed in the meantime. Unlike get_state_synchronize_srcu(),
|
* this function also ensures that any needed SRCU grace period will be
|
* started. This convenience does come at a cost in terms of CPU overhead.
|
*/
|
unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
|
{
|
return srcu_gp_start_if_needed(ssp, NULL, true);
|
}
|
EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
|
|
/**
|
* poll_state_synchronize_srcu - Has cookie's grace period ended?
|
* @ssp: srcu_struct to provide cookie for.
|
* @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu().
|
*
|
* This function takes the cookie that was returned from either
|
* get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and
|
* returns @true if an SRCU grace period elapsed since the time that the
|
* cookie was created.
|
*/
|
bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
|
{
|
if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie))
|
return false;
|
// Ensure that the end of the SRCU grace period happens before
|
// any subsequent code that the caller might execute.
|
smp_mb(); // ^^^
|
return true;
|
}
|
EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
|
|
/*
|
* Callback function for srcu_barrier() use.
|
*/
|
static void srcu_barrier_cb(struct rcu_head *rhp)
|
{
|
struct srcu_data *sdp;
|
struct srcu_struct *ssp;
|
|
sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
|
ssp = sdp->ssp;
|
if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))
|
complete(&ssp->srcu_barrier_completion);
|
}
|
|
/**
|
* srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
|
* @ssp: srcu_struct on which to wait for in-flight callbacks.
|
*/
|
void srcu_barrier(struct srcu_struct *ssp)
|
{
|
int cpu;
|
struct srcu_data *sdp;
|
unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq);
|
|
check_init_srcu_struct(ssp);
|
mutex_lock(&ssp->srcu_barrier_mutex);
|
if (rcu_seq_done(&ssp->srcu_barrier_seq, s)) {
|
smp_mb(); /* Force ordering following return. */
|
mutex_unlock(&ssp->srcu_barrier_mutex);
|
return; /* Someone else did our work for us. */
|
}
|
rcu_seq_start(&ssp->srcu_barrier_seq);
|
init_completion(&ssp->srcu_barrier_completion);
|
|
/* Initial count prevents reaching zero until all CBs are posted. */
|
atomic_set(&ssp->srcu_barrier_cpu_cnt, 1);
|
|
/*
|
* Each pass through this loop enqueues a callback, but only
|
* on CPUs already having callbacks enqueued. Note that if
|
* a CPU already has callbacks enqueue, it must have already
|
* registered the need for a future grace period, so all we
|
* need do is enqueue a callback that will use the same
|
* grace period as the last callback already in the queue.
|
*/
|
for_each_possible_cpu(cpu) {
|
sdp = per_cpu_ptr(ssp->sda, cpu);
|
spin_lock_irq_rcu_node(sdp);
|
atomic_inc(&ssp->srcu_barrier_cpu_cnt);
|
sdp->srcu_barrier_head.func = srcu_barrier_cb;
|
debug_rcu_head_queue(&sdp->srcu_barrier_head);
|
if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
|
&sdp->srcu_barrier_head)) {
|
debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
|
atomic_dec(&ssp->srcu_barrier_cpu_cnt);
|
}
|
spin_unlock_irq_rcu_node(sdp);
|
}
|
|
/* Remove the initial count, at which point reaching zero can happen. */
|
if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))
|
complete(&ssp->srcu_barrier_completion);
|
wait_for_completion(&ssp->srcu_barrier_completion);
|
|
rcu_seq_end(&ssp->srcu_barrier_seq);
|
mutex_unlock(&ssp->srcu_barrier_mutex);
|
}
|
EXPORT_SYMBOL_GPL(srcu_barrier);
|
|
/**
|
* srcu_batches_completed - return batches completed.
|
* @ssp: srcu_struct on which to report batch completion.
|
*
|
* Report the number of batches, correlated with, but not necessarily
|
* precisely the same as, the number of grace periods that have elapsed.
|
*/
|
unsigned long srcu_batches_completed(struct srcu_struct *ssp)
|
{
|
return READ_ONCE(ssp->srcu_idx);
|
}
|
EXPORT_SYMBOL_GPL(srcu_batches_completed);
|
|
/*
|
* Core SRCU state machine. Push state bits of ->srcu_gp_seq
|
* to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has
|
* completed in that state.
|
*/
|
static void srcu_advance_state(struct srcu_struct *ssp)
|
{
|
int idx;
|
|
mutex_lock(&ssp->srcu_gp_mutex);
|
|
/*
|
* Because readers might be delayed for an extended period after
|
* fetching ->srcu_idx for their index, at any point in time there
|
* might well be readers using both idx=0 and idx=1. We therefore
|
* need to wait for readers to clear from both index values before
|
* invoking a callback.
|
*
|
* The load-acquire ensures that we see the accesses performed
|
* by the prior grace period.
|
*/
|
idx = rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq)); /* ^^^ */
|
if (idx == SRCU_STATE_IDLE) {
|
spin_lock_irq_rcu_node(ssp);
|
if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) {
|
WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq));
|
spin_unlock_irq_rcu_node(ssp);
|
mutex_unlock(&ssp->srcu_gp_mutex);
|
return;
|
}
|
idx = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq));
|
if (idx == SRCU_STATE_IDLE)
|
srcu_gp_start(ssp);
|
spin_unlock_irq_rcu_node(ssp);
|
if (idx != SRCU_STATE_IDLE) {
|
mutex_unlock(&ssp->srcu_gp_mutex);
|
return; /* Someone else started the grace period. */
|
}
|
}
|
|
if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
|
idx = 1 ^ (ssp->srcu_idx & 1);
|
if (!try_check_zero(ssp, idx, 1)) {
|
mutex_unlock(&ssp->srcu_gp_mutex);
|
return; /* readers present, retry later. */
|
}
|
srcu_flip(ssp);
|
spin_lock_irq_rcu_node(ssp);
|
rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2);
|
spin_unlock_irq_rcu_node(ssp);
|
}
|
|
if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
|
|
/*
|
* SRCU read-side critical sections are normally short,
|
* so check at least twice in quick succession after a flip.
|
*/
|
idx = 1 ^ (ssp->srcu_idx & 1);
|
if (!try_check_zero(ssp, idx, 2)) {
|
mutex_unlock(&ssp->srcu_gp_mutex);
|
return; /* readers present, retry later. */
|
}
|
srcu_gp_end(ssp); /* Releases ->srcu_gp_mutex. */
|
}
|
}
|
|
/*
|
* Invoke a limited number of SRCU callbacks that have passed through
|
* their grace period. If there are more to do, SRCU will reschedule
|
* the workqueue. Note that needed memory barriers have been executed
|
* in this task's context by srcu_readers_active_idx_check().
|
*/
|
static void srcu_invoke_callbacks(struct work_struct *work)
|
{
|
bool more;
|
struct rcu_cblist ready_cbs;
|
struct rcu_head *rhp;
|
struct srcu_data *sdp;
|
struct srcu_struct *ssp;
|
|
sdp = container_of(work, struct srcu_data, work);
|
|
ssp = sdp->ssp;
|
rcu_cblist_init(&ready_cbs);
|
spin_lock_irq_rcu_node(sdp);
|
rcu_segcblist_advance(&sdp->srcu_cblist,
|
rcu_seq_current(&ssp->srcu_gp_seq));
|
if (sdp->srcu_cblist_invoking ||
|
!rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {
|
spin_unlock_irq_rcu_node(sdp);
|
return; /* Someone else on the job or nothing to do. */
|
}
|
|
/* We are on the job! Extract and invoke ready callbacks. */
|
sdp->srcu_cblist_invoking = true;
|
rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
|
spin_unlock_irq_rcu_node(sdp);
|
rhp = rcu_cblist_dequeue(&ready_cbs);
|
for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
|
debug_rcu_head_unqueue(rhp);
|
local_bh_disable();
|
rhp->func(rhp);
|
local_bh_enable();
|
}
|
|
/*
|
* Update counts, accelerate new callbacks, and if needed,
|
* schedule another round of callback invocation.
|
*/
|
spin_lock_irq_rcu_node(sdp);
|
rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
|
(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
|
rcu_seq_snap(&ssp->srcu_gp_seq));
|
sdp->srcu_cblist_invoking = false;
|
more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
|
spin_unlock_irq_rcu_node(sdp);
|
if (more)
|
srcu_schedule_cbs_sdp(sdp, 0);
|
}
|
|
/*
|
* Finished one round of SRCU grace period. Start another if there are
|
* more SRCU callbacks queued, otherwise put SRCU into not-running state.
|
*/
|
static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay)
|
{
|
bool pushgp = true;
|
|
spin_lock_irq_rcu_node(ssp);
|
if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) {
|
if (!WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq))) {
|
/* All requests fulfilled, time to go idle. */
|
pushgp = false;
|
}
|
} else if (!rcu_seq_state(ssp->srcu_gp_seq)) {
|
/* Outstanding request and no GP. Start one. */
|
srcu_gp_start(ssp);
|
}
|
spin_unlock_irq_rcu_node(ssp);
|
|
if (pushgp)
|
queue_delayed_work(rcu_gp_wq, &ssp->work, delay);
|
}
|
|
/*
|
* This is the work-queue function that handles SRCU grace periods.
|
*/
|
static void process_srcu(struct work_struct *work)
|
{
|
struct srcu_struct *ssp;
|
|
ssp = container_of(work, struct srcu_struct, work.work);
|
|
srcu_advance_state(ssp);
|
srcu_reschedule(ssp, srcu_get_delay(ssp));
|
}
|
|
void srcutorture_get_gp_data(enum rcutorture_type test_type,
|
struct srcu_struct *ssp, int *flags,
|
unsigned long *gp_seq)
|
{
|
if (test_type != SRCU_FLAVOR)
|
return;
|
*flags = 0;
|
*gp_seq = rcu_seq_current(&ssp->srcu_gp_seq);
|
}
|
EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
|
|
void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
|
{
|
int cpu;
|
int idx;
|
unsigned long s0 = 0, s1 = 0;
|
|
idx = ssp->srcu_idx & 0x1;
|
pr_alert("%s%s Tree SRCU g%ld per-CPU(idx=%d):",
|
tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), idx);
|
for_each_possible_cpu(cpu) {
|
unsigned long l0, l1;
|
unsigned long u0, u1;
|
long c0, c1;
|
struct srcu_data *sdp;
|
|
sdp = per_cpu_ptr(ssp->sda, cpu);
|
u0 = data_race(sdp->srcu_unlock_count[!idx]);
|
u1 = data_race(sdp->srcu_unlock_count[idx]);
|
|
/*
|
* Make sure that a lock is always counted if the corresponding
|
* unlock is counted.
|
*/
|
smp_rmb();
|
|
l0 = data_race(sdp->srcu_lock_count[!idx]);
|
l1 = data_race(sdp->srcu_lock_count[idx]);
|
|
c0 = l0 - u0;
|
c1 = l1 - u1;
|
pr_cont(" %d(%ld,%ld %c)",
|
cpu, c0, c1,
|
"C."[rcu_segcblist_empty(&sdp->srcu_cblist)]);
|
s0 += c0;
|
s1 += c1;
|
}
|
pr_cont(" T(%ld,%ld)\n", s0, s1);
|
}
|
EXPORT_SYMBOL_GPL(srcu_torture_stats_print);
|
|
static int __init srcu_bootup_announce(void)
|
{
|
pr_info("Hierarchical SRCU implementation.\n");
|
if (exp_holdoff != DEFAULT_SRCU_EXP_HOLDOFF)
|
pr_info("\tNon-default auto-expedite holdoff of %lu ns.\n", exp_holdoff);
|
return 0;
|
}
|
early_initcall(srcu_bootup_announce);
|
|
void __init srcu_init(void)
|
{
|
struct srcu_struct *ssp;
|
|
srcu_init_done = true;
|
while (!list_empty(&srcu_boot_list)) {
|
ssp = list_first_entry(&srcu_boot_list, struct srcu_struct,
|
work.work.entry);
|
check_init_srcu_struct(ssp);
|
list_del_init(&ssp->work.work.entry);
|
queue_work(rcu_gp_wq, &ssp->work.work);
|
}
|
}
|
|
#ifdef CONFIG_MODULES
|
|
/* Initialize any global-scope srcu_struct structures used by this module. */
|
static int srcu_module_coming(struct module *mod)
|
{
|
int i;
|
struct srcu_struct **sspp = mod->srcu_struct_ptrs;
|
int ret;
|
|
for (i = 0; i < mod->num_srcu_structs; i++) {
|
ret = init_srcu_struct(*(sspp++));
|
if (WARN_ON_ONCE(ret))
|
return ret;
|
}
|
return 0;
|
}
|
|
/* Clean up any global-scope srcu_struct structures used by this module. */
|
static void srcu_module_going(struct module *mod)
|
{
|
int i;
|
struct srcu_struct **sspp = mod->srcu_struct_ptrs;
|
|
for (i = 0; i < mod->num_srcu_structs; i++)
|
cleanup_srcu_struct(*(sspp++));
|
}
|
|
/* Handle one module, either coming or going. */
|
static int srcu_module_notify(struct notifier_block *self,
|
unsigned long val, void *data)
|
{
|
struct module *mod = data;
|
int ret = 0;
|
|
switch (val) {
|
case MODULE_STATE_COMING:
|
ret = srcu_module_coming(mod);
|
break;
|
case MODULE_STATE_GOING:
|
srcu_module_going(mod);
|
break;
|
default:
|
break;
|
}
|
return ret;
|
}
|
|
static struct notifier_block srcu_module_nb = {
|
.notifier_call = srcu_module_notify,
|
.priority = 0,
|
};
|
|
static __init int init_srcu_module_notifier(void)
|
{
|
int ret;
|
|
ret = register_module_notifier(&srcu_module_nb);
|
if (ret)
|
pr_warn("Failed to register srcu module notifier\n");
|
return ret;
|
}
|
late_initcall(init_srcu_module_notifier);
|
|
#endif /* #ifdef CONFIG_MODULES */
|
