v4.19.13 snapshot.
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
new file mode 100644
index 0000000..6c9866a
--- /dev/null
+++ b/kernel/rcu/srcutree.c
@@ -0,0 +1,1310 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2006
+ * Copyright (C) Fujitsu, 2012
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ * Lai Jiangshan <laijs@cn.fujitsu.com>
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU/ *.txt
+ *
+ */
+
+#define pr_fmt(fmt) "rcu: " fmt
+
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/srcu.h>
+
+#include "rcu.h"
+#include "rcu_segcblist.h"
+
+/* Holdoff in nanoseconds for auto-expediting. */
+#define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
+static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
+module_param(exp_holdoff, ulong, 0444);
+
+/* Overflow-check frequency. N bits roughly says every 2**N grace periods. */
+static ulong counter_wrap_check = (ULONG_MAX >> 2);
+module_param(counter_wrap_check, ulong, 0444);
+
+static void srcu_invoke_callbacks(struct work_struct *work);
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
+static void process_srcu(struct work_struct *work);
+
+/* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */
+#define spin_lock_rcu_node(p) \
+do { \
+ spin_lock(&ACCESS_PRIVATE(p, lock)); \
+ smp_mb__after_unlock_lock(); \
+} while (0)
+
+#define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock))
+
+#define spin_lock_irq_rcu_node(p) \
+do { \
+ spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \
+ smp_mb__after_unlock_lock(); \
+} while (0)
+
+#define spin_unlock_irq_rcu_node(p) \
+ spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
+
+#define spin_lock_irqsave_rcu_node(p, flags) \
+do { \
+ spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \
+ smp_mb__after_unlock_lock(); \
+} while (0)
+
+#define spin_unlock_irqrestore_rcu_node(p, flags) \
+ spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \
+
+/*
+ * Initialize SRCU combining tree. Note that statically allocated
+ * srcu_struct structures might already have srcu_read_lock() and
+ * srcu_read_unlock() running against them. So if the is_static parameter
+ * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
+ */
+static void init_srcu_struct_nodes(struct srcu_struct *sp, bool is_static)
+{
+ int cpu;
+ int i;
+ int level = 0;
+ int levelspread[RCU_NUM_LVLS];
+ struct srcu_data *sdp;
+ struct srcu_node *snp;
+ struct srcu_node *snp_first;
+
+ /* Work out the overall tree geometry. */
+ sp->level[0] = &sp->node[0];
+ for (i = 1; i < rcu_num_lvls; i++)
+ sp->level[i] = sp->level[i - 1] + num_rcu_lvl[i - 1];
+ rcu_init_levelspread(levelspread, num_rcu_lvl);
+
+ /* Each pass through this loop initializes one srcu_node structure. */
+ rcu_for_each_node_breadth_first(sp, snp) {
+ spin_lock_init(&ACCESS_PRIVATE(snp, lock));
+ WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=
+ ARRAY_SIZE(snp->srcu_data_have_cbs));
+ for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
+ snp->srcu_have_cbs[i] = 0;
+ snp->srcu_data_have_cbs[i] = 0;
+ }
+ snp->srcu_gp_seq_needed_exp = 0;
+ snp->grplo = -1;
+ snp->grphi = -1;
+ if (snp == &sp->node[0]) {
+ /* Root node, special case. */
+ snp->srcu_parent = NULL;
+ continue;
+ }
+
+ /* Non-root node. */
+ if (snp == sp->level[level + 1])
+ level++;
+ snp->srcu_parent = sp->level[level - 1] +
+ (snp - sp->level[level]) /
+ levelspread[level - 1];
+ }
+
+ /*
+ * Initialize the per-CPU srcu_data array, which feeds into the
+ * leaves of the srcu_node tree.
+ */
+ WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
+ ARRAY_SIZE(sdp->srcu_unlock_count));
+ level = rcu_num_lvls - 1;
+ snp_first = sp->level[level];
+ for_each_possible_cpu(cpu) {
+ sdp = per_cpu_ptr(sp->sda, cpu);
+ spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
+ rcu_segcblist_init(&sdp->srcu_cblist);
+ sdp->srcu_cblist_invoking = false;
+ sdp->srcu_gp_seq_needed = sp->srcu_gp_seq;
+ sdp->srcu_gp_seq_needed_exp = sp->srcu_gp_seq;
+ sdp->mynode = &snp_first[cpu / levelspread[level]];
+ for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
+ if (snp->grplo < 0)
+ snp->grplo = cpu;
+ snp->grphi = cpu;
+ }
+ sdp->cpu = cpu;
+ INIT_DELAYED_WORK(&sdp->work, srcu_invoke_callbacks);
+ sdp->sp = sp;
+ sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
+ if (is_static)
+ continue;
+
+ /* Dynamically allocated, better be no srcu_read_locks()! */
+ for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
+ sdp->srcu_lock_count[i] = 0;
+ sdp->srcu_unlock_count[i] = 0;
+ }
+ }
+}
+
+/*
+ * Initialize non-compile-time initialized fields, including the
+ * associated srcu_node and srcu_data structures. The is_static
+ * parameter is passed through to init_srcu_struct_nodes(), and
+ * also tells us that ->sda has already been wired up to srcu_data.
+ */
+static int init_srcu_struct_fields(struct srcu_struct *sp, bool is_static)
+{
+ mutex_init(&sp->srcu_cb_mutex);
+ mutex_init(&sp->srcu_gp_mutex);
+ sp->srcu_idx = 0;
+ sp->srcu_gp_seq = 0;
+ sp->srcu_barrier_seq = 0;
+ mutex_init(&sp->srcu_barrier_mutex);
+ atomic_set(&sp->srcu_barrier_cpu_cnt, 0);
+ INIT_DELAYED_WORK(&sp->work, process_srcu);
+ if (!is_static)
+ sp->sda = alloc_percpu(struct srcu_data);
+ init_srcu_struct_nodes(sp, is_static);
+ sp->srcu_gp_seq_needed_exp = 0;
+ sp->srcu_last_gp_end = ktime_get_mono_fast_ns();
+ smp_store_release(&sp->srcu_gp_seq_needed, 0); /* Init done. */
+ return sp->sda ? 0 : -ENOMEM;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+ struct lock_class_key *key)
+{
+ /* Don't re-initialize a lock while it is held. */
+ debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+ lockdep_init_map(&sp->dep_map, name, key, 0);
+ spin_lock_init(&ACCESS_PRIVATE(sp, lock));
+ return init_srcu_struct_fields(sp, false);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/**
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @sp: structure to initialize.
+ *
+ * Must invoke this on a given srcu_struct before passing that srcu_struct
+ * to any other function. Each srcu_struct represents a separate domain
+ * of SRCU protection.
+ */
+int init_srcu_struct(struct srcu_struct *sp)
+{
+ spin_lock_init(&ACCESS_PRIVATE(sp, lock));
+ return init_srcu_struct_fields(sp, false);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * First-use initialization of statically allocated srcu_struct
+ * structure. Wiring up the combining tree is more than can be
+ * done with compile-time initialization, so this check is added
+ * to each update-side SRCU primitive. Use sp->lock, which -is-
+ * compile-time initialized, to resolve races involving multiple
+ * CPUs trying to garner first-use privileges.
+ */
+static void check_init_srcu_struct(struct srcu_struct *sp)
+{
+ unsigned long flags;
+
+ WARN_ON_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INIT);
+ /* The smp_load_acquire() pairs with the smp_store_release(). */
+ if (!rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq_needed))) /*^^^*/
+ return; /* Already initialized. */
+ spin_lock_irqsave_rcu_node(sp, flags);
+ if (!rcu_seq_state(sp->srcu_gp_seq_needed)) {
+ spin_unlock_irqrestore_rcu_node(sp, flags);
+ return;
+ }
+ init_srcu_struct_fields(sp, true);
+ spin_unlock_irqrestore_rcu_node(sp, flags);
+}
+
+/*
+ * Returns approximate total of the readers' ->srcu_lock_count[] values
+ * for the rank of per-CPU counters specified by idx.
+ */
+static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
+{
+ int cpu;
+ unsigned long sum = 0;
+
+ for_each_possible_cpu(cpu) {
+ struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
+
+ sum += READ_ONCE(cpuc->srcu_lock_count[idx]);
+ }
+ return sum;
+}
+
+/*
+ * Returns approximate total of the readers' ->srcu_unlock_count[] values
+ * for the rank of per-CPU counters specified by idx.
+ */
+static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
+{
+ int cpu;
+ unsigned long sum = 0;
+
+ for_each_possible_cpu(cpu) {
+ struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
+
+ sum += READ_ONCE(cpuc->srcu_unlock_count[idx]);
+ }
+ return sum;
+}
+
+/*
+ * Return true if the number of pre-existing readers is determined to
+ * be zero.
+ */
+static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
+{
+ unsigned long unlocks;
+
+ unlocks = srcu_readers_unlock_idx(sp, idx);
+
+ /*
+ * Make sure that a lock is always counted if the corresponding
+ * unlock is counted. Needs to be a smp_mb() as the read side may
+ * contain a read from a variable that is written to before the
+ * synchronize_srcu() in the write side. In this case smp_mb()s
+ * A and B act like the store buffering pattern.
+ *
+ * This smp_mb() also pairs with smp_mb() C to prevent accesses
+ * after the synchronize_srcu() from being executed before the
+ * grace period ends.
+ */
+ smp_mb(); /* A */
+
+ /*
+ * If the locks are the same as the unlocks, then there must have
+ * been no readers on this index at some time in between. This does
+ * not mean that there are no more readers, as one could have read
+ * the current index but not have incremented the lock counter yet.
+ *
+ * So suppose that the updater is preempted here for so long
+ * that more than ULONG_MAX non-nested readers come and go in
+ * the meantime. It turns out that this cannot result in overflow
+ * because if a reader modifies its unlock count after we read it
+ * above, then that reader's next load of ->srcu_idx is guaranteed
+ * to get the new value, which will cause it to operate on the
+ * other bank of counters, where it cannot contribute to the
+ * overflow of these counters. This means that there is a maximum
+ * of 2*NR_CPUS increments, which cannot overflow given current
+ * systems, especially not on 64-bit systems.
+ *
+ * OK, how about nesting? This does impose a limit on nesting
+ * of floor(ULONG_MAX/NR_CPUS/2), which should be sufficient,
+ * especially on 64-bit systems.
+ */
+ return srcu_readers_lock_idx(sp, idx) == unlocks;
+}
+
+/**
+ * srcu_readers_active - returns true if there are readers. and false
+ * otherwise
+ * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
+ *
+ * Note that this is not an atomic primitive, and can therefore suffer
+ * severe errors when invoked on an active srcu_struct. That said, it
+ * can be useful as an error check at cleanup time.
+ */
+static bool srcu_readers_active(struct srcu_struct *sp)
+{
+ int cpu;
+ unsigned long sum = 0;
+
+ for_each_possible_cpu(cpu) {
+ struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
+
+ sum += READ_ONCE(cpuc->srcu_lock_count[0]);
+ sum += READ_ONCE(cpuc->srcu_lock_count[1]);
+ sum -= READ_ONCE(cpuc->srcu_unlock_count[0]);
+ sum -= READ_ONCE(cpuc->srcu_unlock_count[1]);
+ }
+ return sum;
+}
+
+#define SRCU_INTERVAL 1
+
+/*
+ * Return grace-period delay, zero if there are expedited grace
+ * periods pending, SRCU_INTERVAL otherwise.
+ */
+static unsigned long srcu_get_delay(struct srcu_struct *sp)
+{
+ if (ULONG_CMP_LT(READ_ONCE(sp->srcu_gp_seq),
+ READ_ONCE(sp->srcu_gp_seq_needed_exp)))
+ return 0;
+ return SRCU_INTERVAL;
+}
+
+/* Helper for cleanup_srcu_struct() and cleanup_srcu_struct_quiesced(). */
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
+{
+ int cpu;
+
+ if (WARN_ON(!srcu_get_delay(sp)))
+ return; /* Just leak it! */
+ if (WARN_ON(srcu_readers_active(sp)))
+ return; /* Just leak it! */
+ if (quiesced) {
+ if (WARN_ON(delayed_work_pending(&sp->work)))
+ return; /* Just leak it! */
+ } else {
+ flush_delayed_work(&sp->work);
+ }
+ for_each_possible_cpu(cpu)
+ if (quiesced) {
+ if (WARN_ON(delayed_work_pending(&per_cpu_ptr(sp->sda, cpu)->work)))
+ return; /* Just leak it! */
+ } else {
+ flush_delayed_work(&per_cpu_ptr(sp->sda, cpu)->work);
+ }
+ if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
+ WARN_ON(srcu_readers_active(sp))) {
+ pr_info("%s: Active srcu_struct %p state: %d\n",
+ __func__, sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
+ return; /* Caller forgot to stop doing call_srcu()? */
+ }
+ free_percpu(sp->sda);
+ sp->sda = NULL;
+}
+EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
+
+/*
+ * Counts the new reader in the appropriate per-CPU element of the
+ * srcu_struct.
+ * Returns an index that must be passed to the matching srcu_read_unlock().
+ */
+int __srcu_read_lock(struct srcu_struct *sp)
+{
+ int idx;
+
+ idx = READ_ONCE(sp->srcu_idx) & 0x1;
+ this_cpu_inc(sp->sda->srcu_lock_count[idx]);
+ smp_mb(); /* B */ /* Avoid leaking the critical section. */
+ return idx;
+}
+EXPORT_SYMBOL_GPL(__srcu_read_lock);
+
+/*
+ * Removes the count for the old reader from the appropriate per-CPU
+ * element of the srcu_struct. Note that this may well be a different
+ * CPU than that which was incremented by the corresponding srcu_read_lock().
+ */
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+{
+ smp_mb(); /* C */ /* Avoid leaking the critical section. */
+ this_cpu_inc(sp->sda->srcu_unlock_count[idx]);
+}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
+
+/*
+ * We use an adaptive strategy for synchronize_srcu() and especially for
+ * synchronize_srcu_expedited(). We spin for a fixed time period
+ * (defined below) to allow SRCU readers to exit their read-side critical
+ * sections. If there are still some readers after a few microseconds,
+ * we repeatedly block for 1-millisecond time periods.
+ */
+#define SRCU_RETRY_CHECK_DELAY 5
+
+/*
+ * Start an SRCU grace period.
+ */
+static void srcu_gp_start(struct srcu_struct *sp)
+{
+ struct srcu_data *sdp = this_cpu_ptr(sp->sda);
+ int state;
+
+ lockdep_assert_held(&ACCESS_PRIVATE(sp, lock));
+ WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));
+ rcu_segcblist_advance(&sdp->srcu_cblist,
+ rcu_seq_current(&sp->srcu_gp_seq));
+ (void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
+ rcu_seq_snap(&sp->srcu_gp_seq));
+ smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
+ rcu_seq_start(&sp->srcu_gp_seq);
+ state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+ WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
+}
+
+/*
+ * Track online CPUs to guide callback workqueue placement.
+ */
+DEFINE_PER_CPU(bool, srcu_online);
+
+void srcu_online_cpu(unsigned int cpu)
+{
+ WRITE_ONCE(per_cpu(srcu_online, cpu), true);
+}
+
+void srcu_offline_cpu(unsigned int cpu)
+{
+ WRITE_ONCE(per_cpu(srcu_online, cpu), false);
+}
+
+/*
+ * Place the workqueue handler on the specified CPU if online, otherwise
+ * just run it whereever. This is useful for placing workqueue handlers
+ * that are to invoke the specified CPU's callbacks.
+ */
+static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
+ struct delayed_work *dwork,
+ unsigned long delay)
+{
+ bool ret;
+
+ preempt_disable();
+ if (READ_ONCE(per_cpu(srcu_online, cpu)))
+ ret = queue_delayed_work_on(cpu, wq, dwork, delay);
+ else
+ ret = queue_delayed_work(wq, dwork, delay);
+ preempt_enable();
+ return ret;
+}
+
+/*
+ * Schedule callback invocation for the specified srcu_data structure,
+ * if possible, on the corresponding CPU.
+ */
+static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
+{
+ srcu_queue_delayed_work_on(sdp->cpu, rcu_gp_wq, &sdp->work, delay);
+}
+
+/*
+ * Schedule callback invocation for all srcu_data structures associated
+ * with the specified srcu_node structure that have callbacks for the
+ * just-completed grace period, the one corresponding to idx. If possible,
+ * schedule this invocation on the corresponding CPUs.
+ */
+static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp,
+ unsigned long mask, unsigned long delay)
+{
+ int cpu;
+
+ for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
+ if (!(mask & (1 << (cpu - snp->grplo))))
+ continue;
+ srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), delay);
+ }
+}
+
+/*
+ * Note the end of an SRCU grace period. Initiates callback invocation
+ * and starts a new grace period if needed.
+ *
+ * The ->srcu_cb_mutex acquisition does not protect any data, but
+ * instead prevents more than one grace period from starting while we
+ * 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 *sp)
+{
+ unsigned long cbdelay;
+ bool cbs;
+ bool last_lvl;
+ int cpu;
+ unsigned long flags;
+ unsigned long gpseq;
+ int idx;
+ unsigned long mask;
+ struct srcu_data *sdp;
+ struct srcu_node *snp;
+
+ /* Prevent more than one additional grace period. */
+ mutex_lock(&sp->srcu_cb_mutex);
+
+ /* End the current grace period. */
+ spin_lock_irq_rcu_node(sp);
+ idx = rcu_seq_state(sp->srcu_gp_seq);
+ WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
+ cbdelay = srcu_get_delay(sp);
+ sp->srcu_last_gp_end = ktime_get_mono_fast_ns();
+ rcu_seq_end(&sp->srcu_gp_seq);
+ gpseq = rcu_seq_current(&sp->srcu_gp_seq);
+ if (ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, gpseq))
+ sp->srcu_gp_seq_needed_exp = gpseq;
+ spin_unlock_irq_rcu_node(sp);
+ mutex_unlock(&sp->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);
+ rcu_for_each_node_breadth_first(sp, snp) {
+ spin_lock_irq_rcu_node(snp);
+ cbs = false;
+ last_lvl = snp >= sp->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))
+ 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(sp, 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(sp->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(&sp->srcu_cb_mutex);
+
+ /* Start a new grace period if needed. */
+ spin_lock_irq_rcu_node(sp);
+ gpseq = rcu_seq_current(&sp->srcu_gp_seq);
+ if (!rcu_seq_state(gpseq) &&
+ ULONG_CMP_LT(gpseq, sp->srcu_gp_seq_needed)) {
+ srcu_gp_start(sp);
+ spin_unlock_irq_rcu_node(sp);
+ srcu_reschedule(sp, 0);
+ } else {
+ spin_unlock_irq_rcu_node(sp);
+ }
+}
+
+/*
+ * 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 *sp, struct srcu_node *snp,
+ unsigned long s)
+{
+ unsigned long flags;
+
+ for (; snp != NULL; snp = snp->srcu_parent) {
+ if (rcu_seq_done(&sp->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(sp, flags);
+ if (ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, s))
+ sp->srcu_gp_seq_needed_exp = s;
+ spin_unlock_irqrestore_rcu_node(sp, 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 *sp, 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(&sp->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(sp, 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))
+ 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(sp, flags);
+ if (ULONG_CMP_LT(sp->srcu_gp_seq_needed, s)) {
+ /*
+ * Record need for grace period s. Pair with load
+ * acquire setting up for initialization.
+ */
+ smp_store_release(&sp->srcu_gp_seq_needed, s); /*^^^*/
+ }
+ if (!do_norm && ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, s))
+ sp->srcu_gp_seq_needed_exp = s;
+
+ /* If grace period not already done and none in progress, start it. */
+ if (!rcu_seq_done(&sp->srcu_gp_seq, s) &&
+ rcu_seq_state(sp->srcu_gp_seq) == SRCU_STATE_IDLE) {
+ WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));
+ srcu_gp_start(sp);
+ queue_delayed_work(rcu_gp_wq, &sp->work, srcu_get_delay(sp));
+ }
+ spin_unlock_irqrestore_rcu_node(sp, 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 *sp, int idx, int trycount)
+{
+ for (;;) {
+ if (srcu_readers_active_idx_check(sp, idx))
+ return true;
+ if (--trycount + !srcu_get_delay(sp) <= 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 *sp)
+{
+ /*
+ * 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(sp->srcu_idx, sp->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 amoritized 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 *sp)
+{
+ unsigned long curseq;
+ unsigned long flags;
+ struct srcu_data *sdp;
+ unsigned long t;
+
+ /* If the local srcu_data structure has callbacks, not idle. */
+ local_irq_save(flags);
+ sdp = this_cpu_ptr(sp->sda);
+ if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
+ local_irq_restore(flags);
+ return false; /* Callbacks already present, so not idle. */
+ }
+ local_irq_restore(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();
+ if (exp_holdoff == 0 ||
+ time_in_range_open(t, sp->srcu_last_gp_end,
+ sp->srcu_last_gp_end + exp_holdoff))
+ return false; /* Too soon after last GP. */
+
+ /* Next, check for probable idleness. */
+ curseq = rcu_seq_current(&sp->srcu_gp_seq);
+ smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */
+ if (ULONG_CMP_LT(curseq, READ_ONCE(sp->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(&sp->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)
+{
+}
+
+/*
+ * 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.
+ */
+void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
+ rcu_callback_t func, bool do_norm)
+{
+ unsigned long flags;
+ bool needexp = false;
+ bool needgp = false;
+ unsigned long s;
+ struct srcu_data *sdp;
+
+ check_init_srcu_struct(sp);
+ 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;
+ local_irq_save(flags);
+ sdp = this_cpu_ptr(sp->sda);
+ spin_lock_rcu_node(sdp);
+ rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false);
+ rcu_segcblist_advance(&sdp->srcu_cblist,
+ rcu_seq_current(&sp->srcu_gp_seq));
+ s = rcu_seq_snap(&sp->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(sp, sdp, s, do_norm);
+ else if (needexp)
+ srcu_funnel_exp_start(sp, sdp->mynode, s);
+}
+
+/**
+ * call_srcu() - Queue a callback for invocation after an SRCU grace period
+ * @sp: 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 *sp, struct rcu_head *rhp,
+ rcu_callback_t func)
+{
+ __call_srcu(sp, rhp, func, true);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
+
+/*
+ * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
+ */
+static void __synchronize_srcu(struct srcu_struct *sp, bool do_norm)
+{
+ struct rcu_synchronize rcu;
+
+ RCU_LOCKDEP_WARN(lock_is_held(&sp->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(sp);
+ init_completion(&rcu.completion);
+ init_rcu_head_on_stack(&rcu.head);
+ __call_srcu(sp, &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
+ * @sp: 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 *sp)
+{
+ __synchronize_srcu(sp, rcu_gp_is_normal());
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ * @sp: 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-sched 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 *sp)
+{
+ if (srcu_might_be_idle(sp) || rcu_gp_is_expedited())
+ synchronize_srcu_expedited(sp);
+ else
+ __synchronize_srcu(sp, true);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
+
+/*
+ * Callback function for srcu_barrier() use.
+ */
+static void srcu_barrier_cb(struct rcu_head *rhp)
+{
+ struct srcu_data *sdp;
+ struct srcu_struct *sp;
+
+ sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
+ sp = sdp->sp;
+ if (atomic_dec_and_test(&sp->srcu_barrier_cpu_cnt))
+ complete(&sp->srcu_barrier_completion);
+}
+
+/**
+ * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
+ * @sp: srcu_struct on which to wait for in-flight callbacks.
+ */
+void srcu_barrier(struct srcu_struct *sp)
+{
+ int cpu;
+ struct srcu_data *sdp;
+ unsigned long s = rcu_seq_snap(&sp->srcu_barrier_seq);
+
+ check_init_srcu_struct(sp);
+ mutex_lock(&sp->srcu_barrier_mutex);
+ if (rcu_seq_done(&sp->srcu_barrier_seq, s)) {
+ smp_mb(); /* Force ordering following return. */
+ mutex_unlock(&sp->srcu_barrier_mutex);
+ return; /* Someone else did our work for us. */
+ }
+ rcu_seq_start(&sp->srcu_barrier_seq);
+ init_completion(&sp->srcu_barrier_completion);
+
+ /* Initial count prevents reaching zero until all CBs are posted. */
+ atomic_set(&sp->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(sp->sda, cpu);
+ spin_lock_irq_rcu_node(sdp);
+ atomic_inc(&sp->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, 0)) {
+ debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
+ atomic_dec(&sp->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(&sp->srcu_barrier_cpu_cnt))
+ complete(&sp->srcu_barrier_completion);
+ wait_for_completion(&sp->srcu_barrier_completion);
+
+ rcu_seq_end(&sp->srcu_barrier_seq);
+ mutex_unlock(&sp->srcu_barrier_mutex);
+}
+EXPORT_SYMBOL_GPL(srcu_barrier);
+
+/**
+ * srcu_batches_completed - return batches completed.
+ * @sp: 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 *sp)
+{
+ return sp->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 *sp)
+{
+ int idx;
+
+ mutex_lock(&sp->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(&sp->srcu_gp_seq)); /* ^^^ */
+ if (idx == SRCU_STATE_IDLE) {
+ spin_lock_irq_rcu_node(sp);
+ if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {
+ WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq));
+ spin_unlock_irq_rcu_node(sp);
+ mutex_unlock(&sp->srcu_gp_mutex);
+ return;
+ }
+ idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+ if (idx == SRCU_STATE_IDLE)
+ srcu_gp_start(sp);
+ spin_unlock_irq_rcu_node(sp);
+ if (idx != SRCU_STATE_IDLE) {
+ mutex_unlock(&sp->srcu_gp_mutex);
+ return; /* Someone else started the grace period. */
+ }
+ }
+
+ if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
+ idx = 1 ^ (sp->srcu_idx & 1);
+ if (!try_check_zero(sp, idx, 1)) {
+ mutex_unlock(&sp->srcu_gp_mutex);
+ return; /* readers present, retry later. */
+ }
+ srcu_flip(sp);
+ rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
+ }
+
+ if (rcu_seq_state(READ_ONCE(sp->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 ^ (sp->srcu_idx & 1);
+ if (!try_check_zero(sp, idx, 2)) {
+ mutex_unlock(&sp->srcu_gp_mutex);
+ return; /* readers present, retry later. */
+ }
+ srcu_gp_end(sp); /* 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 *sp;
+
+ sdp = container_of(work, struct srcu_data, work.work);
+ sp = sdp->sp;
+ rcu_cblist_init(&ready_cbs);
+ spin_lock_irq_rcu_node(sdp);
+ rcu_segcblist_advance(&sdp->srcu_cblist,
+ rcu_seq_current(&sp->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(&sp->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 *sp, unsigned long delay)
+{
+ bool pushgp = true;
+
+ spin_lock_irq_rcu_node(sp);
+ if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {
+ if (!WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq))) {
+ /* All requests fulfilled, time to go idle. */
+ pushgp = false;
+ }
+ } else if (!rcu_seq_state(sp->srcu_gp_seq)) {
+ /* Outstanding request and no GP. Start one. */
+ srcu_gp_start(sp);
+ }
+ spin_unlock_irq_rcu_node(sp);
+
+ if (pushgp)
+ queue_delayed_work(rcu_gp_wq, &sp->work, delay);
+}
+
+/*
+ * This is the work-queue function that handles SRCU grace periods.
+ */
+static void process_srcu(struct work_struct *work)
+{
+ struct srcu_struct *sp;
+
+ sp = container_of(work, struct srcu_struct, work.work);
+
+ srcu_advance_state(sp);
+ srcu_reschedule(sp, srcu_get_delay(sp));
+}
+
+void srcutorture_get_gp_data(enum rcutorture_type test_type,
+ struct srcu_struct *sp, int *flags,
+ unsigned long *gp_seq)
+{
+ if (test_type != SRCU_FLAVOR)
+ return;
+ *flags = 0;
+ *gp_seq = rcu_seq_current(&sp->srcu_gp_seq);
+}
+EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
+
+void srcu_torture_stats_print(struct srcu_struct *sp, char *tt, char *tf)
+{
+ int cpu;
+ int idx;
+ unsigned long s0 = 0, s1 = 0;
+
+ idx = sp->srcu_idx & 0x1;
+ pr_alert("%s%s Tree SRCU g%ld per-CPU(idx=%d):",
+ tt, tf, rcu_seq_current(&sp->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(sp->sda, cpu);
+ u0 = sdp->srcu_unlock_count[!idx];
+ u1 = sdp->srcu_unlock_count[idx];
+
+ /*
+ * Make sure that a lock is always counted if the corresponding
+ * unlock is counted.
+ */
+ smp_rmb();
+
+ l0 = sdp->srcu_lock_count[!idx];
+ l1 = sdp->srcu_lock_count[idx];
+
+ c0 = l0 - u0;
+ c1 = l1 - u1;
+ pr_cont(" %d(%ld,%ld %1p)",
+ cpu, c0, c1, rcu_segcblist_head(&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);