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Message-Id: <1466027173-5501-4-git-send-email-paulmck@linux.vnet.ibm.com>
Date: Wed, 15 Jun 2016 14:46:05 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 04/12] rcu: Move expedited code from tree.c to tree_exp.h
People have been having some difficulty finding their way around the
RCU code. This commit therefore pulls some of the expedited grace-period
code from tree.c to a new tree_exp.h file. This commit is strictly code
movement, with the exception of a forward declaration that was added
for the sync_sched_exp_online_cleanup() function.
A subsequent commit will move the remaining expedited grace-period code
from tree_plugin.h to tree_exp.h.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/tree.c | 545 +-----------------------------------------------
kernel/rcu/tree_exp.h | 564 ++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 566 insertions(+), 543 deletions(-)
create mode 100644 kernel/rcu/tree_exp.h
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4aefeafb9a95..c844b6142a86 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -159,6 +159,7 @@ static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
static void rcu_report_exp_rdp(struct rcu_state *rsp,
struct rcu_data *rdp, bool wake);
+static void sync_sched_exp_online_cleanup(int cpu);
/* rcuc/rcub kthread realtime priority */
#ifdef CONFIG_RCU_KTHREAD_PRIO
@@ -3447,549 +3448,6 @@ static bool rcu_seq_done(unsigned long *sp, unsigned long s)
return ULONG_CMP_GE(READ_ONCE(*sp), s);
}
-/* Wrapper functions for expedited grace periods. */
-static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
-{
- rcu_seq_start(&rsp->expedited_sequence);
-}
-static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
-{
- rcu_seq_end(&rsp->expedited_sequence);
- smp_mb(); /* Ensure that consecutive grace periods serialize. */
-}
-static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
-{
- unsigned long s;
-
- smp_mb(); /* Caller's modifications seen first by other CPUs. */
- s = rcu_seq_snap(&rsp->expedited_sequence);
- trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
- return s;
-}
-static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
-{
- return rcu_seq_done(&rsp->expedited_sequence, s);
-}
-
-/*
- * Reset the ->expmaskinit values in the rcu_node tree to reflect any
- * recent CPU-online activity. Note that these masks are not cleared
- * when CPUs go offline, so they reflect the union of all CPUs that have
- * ever been online. This means that this function normally takes its
- * no-work-to-do fastpath.
- */
-static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
-{
- bool done;
- unsigned long flags;
- unsigned long mask;
- unsigned long oldmask;
- int ncpus = READ_ONCE(rsp->ncpus);
- struct rcu_node *rnp;
- struct rcu_node *rnp_up;
-
- /* If no new CPUs onlined since last time, nothing to do. */
- if (likely(ncpus == rsp->ncpus_snap))
- return;
- rsp->ncpus_snap = ncpus;
-
- /*
- * Each pass through the following loop propagates newly onlined
- * CPUs for the current rcu_node structure up the rcu_node tree.
- */
- rcu_for_each_leaf_node(rsp, rnp) {
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- if (rnp->expmaskinit == rnp->expmaskinitnext) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- continue; /* No new CPUs, nothing to do. */
- }
-
- /* Update this node's mask, track old value for propagation. */
- oldmask = rnp->expmaskinit;
- rnp->expmaskinit = rnp->expmaskinitnext;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-
- /* If was already nonzero, nothing to propagate. */
- if (oldmask)
- continue;
-
- /* Propagate the new CPU up the tree. */
- mask = rnp->grpmask;
- rnp_up = rnp->parent;
- done = false;
- while (rnp_up) {
- raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
- if (rnp_up->expmaskinit)
- done = true;
- rnp_up->expmaskinit |= mask;
- raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
- if (done)
- break;
- mask = rnp_up->grpmask;
- rnp_up = rnp_up->parent;
- }
- }
-}
-
-/*
- * Reset the ->expmask values in the rcu_node tree in preparation for
- * a new expedited grace period.
- */
-static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
-{
- unsigned long flags;
- struct rcu_node *rnp;
-
- sync_exp_reset_tree_hotplug(rsp);
- rcu_for_each_node_breadth_first(rsp, rnp) {
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- WARN_ON_ONCE(rnp->expmask);
- rnp->expmask = rnp->expmaskinit;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
-}
-
-/*
- * Return non-zero if there is no RCU expedited grace period in progress
- * for the specified rcu_node structure, in other words, if all CPUs and
- * tasks covered by the specified rcu_node structure have done their bit
- * for the current expedited grace period. Works only for preemptible
- * RCU -- other RCU implementation use other means.
- *
- * Caller must hold the rcu_state's exp_mutex.
- */
-static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
-{
- return rnp->exp_tasks == NULL &&
- READ_ONCE(rnp->expmask) == 0;
-}
-
-/*
- * Report the exit from RCU read-side critical section for the last task
- * that queued itself during or before the current expedited preemptible-RCU
- * grace period. This event is reported either to the rcu_node structure on
- * which the task was queued or to one of that rcu_node structure's ancestors,
- * recursively up the tree. (Calm down, calm down, we do the recursion
- * iteratively!)
- *
- * Caller must hold the rcu_state's exp_mutex and the specified rcu_node
- * structure's ->lock.
- */
-static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
- bool wake, unsigned long flags)
- __releases(rnp->lock)
-{
- unsigned long mask;
-
- for (;;) {
- if (!sync_rcu_preempt_exp_done(rnp)) {
- if (!rnp->expmask)
- rcu_initiate_boost(rnp, flags);
- else
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- break;
- }
- if (rnp->parent == NULL) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- if (wake) {
- smp_mb(); /* EGP done before wake_up(). */
- swake_up(&rsp->expedited_wq);
- }
- break;
- }
- mask = rnp->grpmask;
- raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
- rnp = rnp->parent;
- raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
- WARN_ON_ONCE(!(rnp->expmask & mask));
- rnp->expmask &= ~mask;
- }
-}
-
-/*
- * Report expedited quiescent state for specified node. This is a
- * lock-acquisition wrapper function for __rcu_report_exp_rnp().
- *
- * Caller must hold the rcu_state's exp_mutex.
- */
-static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
- struct rcu_node *rnp, bool wake)
-{
- unsigned long flags;
-
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- __rcu_report_exp_rnp(rsp, rnp, wake, flags);
-}
-
-/*
- * Report expedited quiescent state for multiple CPUs, all covered by the
- * specified leaf rcu_node structure. Caller must hold the rcu_state's
- * exp_mutex.
- */
-static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
- unsigned long mask, bool wake)
-{
- unsigned long flags;
-
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- if (!(rnp->expmask & mask)) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return;
- }
- rnp->expmask &= ~mask;
- __rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
-}
-
-/*
- * Report expedited quiescent state for specified rcu_data (CPU).
- */
-static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
- bool wake)
-{
- rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
-}
-
-/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
-static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,
- unsigned long s)
-{
- if (rcu_exp_gp_seq_done(rsp, s)) {
- trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
- /* Ensure test happens before caller kfree(). */
- smp_mb__before_atomic(); /* ^^^ */
- atomic_long_inc(stat);
- return true;
- }
- return false;
-}
-
-/*
- * Funnel-lock acquisition for expedited grace periods. Returns true
- * if some other task completed an expedited grace period that this task
- * can piggy-back on, and with no mutex held. Otherwise, returns false
- * with the mutex held, indicating that the caller must actually do the
- * expedited grace period.
- */
-static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
-{
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
- struct rcu_node *rnp = rdp->mynode;
- struct rcu_node *rnp_root = rcu_get_root(rsp);
-
- /* Low-contention fastpath. */
- if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
- (rnp == rnp_root ||
- ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
- !mutex_is_locked(&rsp->exp_mutex) &&
- mutex_trylock(&rsp->exp_mutex))
- goto fastpath;
-
- /*
- * Each pass through the following loop works its way up
- * the rcu_node tree, returning if others have done the work or
- * otherwise falls through to acquire rsp->exp_mutex. The mapping
- * from CPU to rcu_node structure can be inexact, as it is just
- * promoting locality and is not strictly needed for correctness.
- */
- for (; rnp != NULL; rnp = rnp->parent) {
- if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))
- return true;
-
- /* Work not done, either wait here or go up. */
- spin_lock(&rnp->exp_lock);
- if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
-
- /* Someone else doing GP, so wait for them. */
- spin_unlock(&rnp->exp_lock);
- trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
- rnp->grplo, rnp->grphi,
- TPS("wait"));
- wait_event(rnp->exp_wq[(s >> 1) & 0x3],
- sync_exp_work_done(rsp,
- &rdp->exp_workdone2, s));
- return true;
- }
- rnp->exp_seq_rq = s; /* Followers can wait on us. */
- spin_unlock(&rnp->exp_lock);
- trace_rcu_exp_funnel_lock(rsp->name, rnp->level, rnp->grplo,
- rnp->grphi, TPS("nxtlvl"));
- }
- mutex_lock(&rsp->exp_mutex);
-fastpath:
- if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
- mutex_unlock(&rsp->exp_mutex);
- return true;
- }
- rcu_exp_gp_seq_start(rsp);
- trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));
- return false;
-}
-
-/* Invoked on each online non-idle CPU for expedited quiescent state. */
-static void sync_sched_exp_handler(void *data)
-{
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp = data;
-
- rdp = this_cpu_ptr(rsp->rda);
- rnp = rdp->mynode;
- if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
- __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
- return;
- if (rcu_is_cpu_rrupt_from_idle()) {
- rcu_report_exp_rdp(&rcu_sched_state,
- this_cpu_ptr(&rcu_sched_data), true);
- return;
- }
- __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
- resched_cpu(smp_processor_id());
-}
-
-/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
-static void sync_sched_exp_online_cleanup(int cpu)
-{
- struct rcu_data *rdp;
- int ret;
- struct rcu_node *rnp;
- struct rcu_state *rsp = &rcu_sched_state;
-
- rdp = per_cpu_ptr(rsp->rda, cpu);
- rnp = rdp->mynode;
- if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
- return;
- ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
- WARN_ON_ONCE(ret);
-}
-
-/*
- * Select the nodes that the upcoming expedited grace period needs
- * to wait for.
- */
-static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
- smp_call_func_t func)
-{
- int cpu;
- unsigned long flags;
- unsigned long mask;
- unsigned long mask_ofl_test;
- unsigned long mask_ofl_ipi;
- int ret;
- struct rcu_node *rnp;
-
- sync_exp_reset_tree(rsp);
- rcu_for_each_leaf_node(rsp, rnp) {
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
-
- /* Each pass checks a CPU for identity, offline, and idle. */
- mask_ofl_test = 0;
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
-
- if (raw_smp_processor_id() == cpu ||
- !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
- mask_ofl_test |= rdp->grpmask;
- }
- mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
-
- /*
- * Need to wait for any blocked tasks as well. Note that
- * additional blocking tasks will also block the expedited
- * GP until such time as the ->expmask bits are cleared.
- */
- if (rcu_preempt_has_tasks(rnp))
- rnp->exp_tasks = rnp->blkd_tasks.next;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-
- /* IPI the remaining CPUs for expedited quiescent state. */
- mask = 1;
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
- if (!(mask_ofl_ipi & mask))
- continue;
-retry_ipi:
- ret = smp_call_function_single(cpu, func, rsp, 0);
- if (!ret) {
- mask_ofl_ipi &= ~mask;
- continue;
- }
- /* Failed, raced with offline. */
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- if (cpu_online(cpu) &&
- (rnp->expmask & mask)) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- schedule_timeout_uninterruptible(1);
- if (cpu_online(cpu) &&
- (rnp->expmask & mask))
- goto retry_ipi;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- }
- if (!(rnp->expmask & mask))
- mask_ofl_ipi &= ~mask;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- /* Report quiescent states for those that went offline. */
- mask_ofl_test |= mask_ofl_ipi;
- if (mask_ofl_test)
- rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
- }
-}
-
-static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
-{
- int cpu;
- unsigned long jiffies_stall;
- unsigned long jiffies_start;
- unsigned long mask;
- int ndetected;
- struct rcu_node *rnp;
- struct rcu_node *rnp_root = rcu_get_root(rsp);
- int ret;
-
- jiffies_stall = rcu_jiffies_till_stall_check();
- jiffies_start = jiffies;
-
- for (;;) {
- ret = swait_event_timeout(
- rsp->expedited_wq,
- sync_rcu_preempt_exp_done(rnp_root),
- jiffies_stall);
- if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
- return;
- if (ret < 0) {
- /* Hit a signal, disable CPU stall warnings. */
- swait_event(rsp->expedited_wq,
- sync_rcu_preempt_exp_done(rnp_root));
- return;
- }
- pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
- rsp->name);
- ndetected = 0;
- rcu_for_each_leaf_node(rsp, rnp) {
- ndetected += rcu_print_task_exp_stall(rnp);
- mask = 1;
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
- struct rcu_data *rdp;
-
- if (!(rnp->expmask & mask))
- continue;
- ndetected++;
- rdp = per_cpu_ptr(rsp->rda, cpu);
- pr_cont(" %d-%c%c%c", cpu,
- "O."[!!cpu_online(cpu)],
- "o."[!!(rdp->grpmask & rnp->expmaskinit)],
- "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
- }
- mask <<= 1;
- }
- pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
- jiffies - jiffies_start, rsp->expedited_sequence,
- rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
- if (ndetected) {
- pr_err("blocking rcu_node structures:");
- rcu_for_each_node_breadth_first(rsp, rnp) {
- if (rnp == rnp_root)
- continue; /* printed unconditionally */
- if (sync_rcu_preempt_exp_done(rnp))
- continue;
- pr_cont(" l=%u:%d-%d:%#lx/%c",
- rnp->level, rnp->grplo, rnp->grphi,
- rnp->expmask,
- ".T"[!!rnp->exp_tasks]);
- }
- pr_cont("\n");
- }
- rcu_for_each_leaf_node(rsp, rnp) {
- mask = 1;
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
- if (!(rnp->expmask & mask))
- continue;
- dump_cpu_task(cpu);
- }
- }
- jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
- }
-}
-
-/*
- * Wait for the current expedited grace period to complete, and then
- * wake up everyone who piggybacked on the just-completed expedited
- * grace period. Also update all the ->exp_seq_rq counters as needed
- * in order to avoid counter-wrap problems.
- */
-static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
-{
- struct rcu_node *rnp;
-
- synchronize_sched_expedited_wait(rsp);
- rcu_exp_gp_seq_end(rsp);
- trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));
-
- /*
- * Switch over to wakeup mode, allowing the next GP, but -only- the
- * next GP, to proceed.
- */
- mutex_lock(&rsp->exp_wake_mutex);
- mutex_unlock(&rsp->exp_mutex);
-
- rcu_for_each_node_breadth_first(rsp, rnp) {
- if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
- spin_lock(&rnp->exp_lock);
- /* Recheck, avoid hang in case someone just arrived. */
- if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
- rnp->exp_seq_rq = s;
- spin_unlock(&rnp->exp_lock);
- }
- wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
- }
- trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
- mutex_unlock(&rsp->exp_wake_mutex);
-}
-
-/**
- * synchronize_sched_expedited - Brute-force RCU-sched grace period
- *
- * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
- * approach to force the grace period to end quickly. This consumes
- * significant time on all CPUs and is unfriendly to real-time workloads,
- * so is thus not recommended for any sort of common-case code. In fact,
- * if you are using synchronize_sched_expedited() in a loop, please
- * restructure your code to batch your updates, and then use a single
- * synchronize_sched() instead.
- *
- * This implementation can be thought of as an application of sequence
- * locking to expedited grace periods, but using the sequence counter to
- * determine when someone else has already done the work instead of for
- * retrying readers.
- */
-void synchronize_sched_expedited(void)
-{
- unsigned long s;
- struct rcu_state *rsp = &rcu_sched_state;
-
- /* If only one CPU, this is automatically a grace period. */
- if (rcu_blocking_is_gp())
- return;
-
- /* If expedited grace periods are prohibited, fall back to normal. */
- if (rcu_gp_is_normal()) {
- wait_rcu_gp(call_rcu_sched);
- return;
- }
-
- /* Take a snapshot of the sequence number. */
- s = rcu_exp_gp_seq_snap(rsp);
- if (exp_funnel_lock(rsp, s))
- return; /* Someone else did our work for us. */
-
- /* Initialize the rcu_node tree in preparation for the wait. */
- sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
-
- /* Wait and clean up, including waking everyone. */
- rcu_exp_wait_wake(rsp, s);
-}
-EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
-
/*
* Check to see if there is any immediate RCU-related work to be done
* by the current CPU, for the specified type of RCU, returning 1 if so.
@@ -4747,4 +4205,5 @@ void __init rcu_init(void)
rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
}
+#include "tree_exp.h"
#include "tree_plugin.h"
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
new file mode 100644
index 000000000000..db0909cf7fe1
--- /dev/null
+++ b/kernel/rcu/tree_exp.h
@@ -0,0 +1,564 @@
+/*
+ * RCU expedited grace periods
+ *
+ * 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 IBM Corporation, 2016
+ *
+ * Authors: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
+ */
+
+/* Wrapper functions for expedited grace periods. */
+static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
+{
+ rcu_seq_start(&rsp->expedited_sequence);
+}
+static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
+{
+ rcu_seq_end(&rsp->expedited_sequence);
+ smp_mb(); /* Ensure that consecutive grace periods serialize. */
+}
+static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
+{
+ unsigned long s;
+
+ smp_mb(); /* Caller's modifications seen first by other CPUs. */
+ s = rcu_seq_snap(&rsp->expedited_sequence);
+ trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
+ return s;
+}
+static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
+{
+ return rcu_seq_done(&rsp->expedited_sequence, s);
+}
+
+/*
+ * Reset the ->expmaskinit values in the rcu_node tree to reflect any
+ * recent CPU-online activity. Note that these masks are not cleared
+ * when CPUs go offline, so they reflect the union of all CPUs that have
+ * ever been online. This means that this function normally takes its
+ * no-work-to-do fastpath.
+ */
+static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
+{
+ bool done;
+ unsigned long flags;
+ unsigned long mask;
+ unsigned long oldmask;
+ int ncpus = READ_ONCE(rsp->ncpus);
+ struct rcu_node *rnp;
+ struct rcu_node *rnp_up;
+
+ /* If no new CPUs onlined since last time, nothing to do. */
+ if (likely(ncpus == rsp->ncpus_snap))
+ return;
+ rsp->ncpus_snap = ncpus;
+
+ /*
+ * Each pass through the following loop propagates newly onlined
+ * CPUs for the current rcu_node structure up the rcu_node tree.
+ */
+ rcu_for_each_leaf_node(rsp, rnp) {
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (rnp->expmaskinit == rnp->expmaskinitnext) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ continue; /* No new CPUs, nothing to do. */
+ }
+
+ /* Update this node's mask, track old value for propagation. */
+ oldmask = rnp->expmaskinit;
+ rnp->expmaskinit = rnp->expmaskinitnext;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+ /* If was already nonzero, nothing to propagate. */
+ if (oldmask)
+ continue;
+
+ /* Propagate the new CPU up the tree. */
+ mask = rnp->grpmask;
+ rnp_up = rnp->parent;
+ done = false;
+ while (rnp_up) {
+ raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
+ if (rnp_up->expmaskinit)
+ done = true;
+ rnp_up->expmaskinit |= mask;
+ raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
+ if (done)
+ break;
+ mask = rnp_up->grpmask;
+ rnp_up = rnp_up->parent;
+ }
+ }
+}
+
+/*
+ * Reset the ->expmask values in the rcu_node tree in preparation for
+ * a new expedited grace period.
+ */
+static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
+{
+ unsigned long flags;
+ struct rcu_node *rnp;
+
+ sync_exp_reset_tree_hotplug(rsp);
+ rcu_for_each_node_breadth_first(rsp, rnp) {
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ WARN_ON_ONCE(rnp->expmask);
+ rnp->expmask = rnp->expmaskinit;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
+}
+
+/*
+ * Return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period. Works only for preemptible
+ * RCU -- other RCU implementation use other means.
+ *
+ * Caller must hold the rcu_state's exp_mutex.
+ */
+static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
+{
+ return rnp->exp_tasks == NULL &&
+ READ_ONCE(rnp->expmask) == 0;
+}
+
+/*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period. This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree. (Calm down, calm down, we do the recursion
+ * iteratively!)
+ *
+ * Caller must hold the rcu_state's exp_mutex and the specified rcu_node
+ * structure's ->lock.
+ */
+static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+ bool wake, unsigned long flags)
+ __releases(rnp->lock)
+{
+ unsigned long mask;
+
+ for (;;) {
+ if (!sync_rcu_preempt_exp_done(rnp)) {
+ if (!rnp->expmask)
+ rcu_initiate_boost(rnp, flags);
+ else
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ break;
+ }
+ if (rnp->parent == NULL) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ if (wake) {
+ smp_mb(); /* EGP done before wake_up(). */
+ swake_up(&rsp->expedited_wq);
+ }
+ break;
+ }
+ mask = rnp->grpmask;
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
+ rnp = rnp->parent;
+ raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
+ WARN_ON_ONCE(!(rnp->expmask & mask));
+ rnp->expmask &= ~mask;
+ }
+}
+
+/*
+ * Report expedited quiescent state for specified node. This is a
+ * lock-acquisition wrapper function for __rcu_report_exp_rnp().
+ *
+ * Caller must hold the rcu_state's exp_mutex.
+ */
+static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
+ struct rcu_node *rnp, bool wake)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ __rcu_report_exp_rnp(rsp, rnp, wake, flags);
+}
+
+/*
+ * Report expedited quiescent state for multiple CPUs, all covered by the
+ * specified leaf rcu_node structure. Caller must hold the rcu_state's
+ * exp_mutex.
+ */
+static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
+ unsigned long mask, bool wake)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (!(rnp->expmask & mask)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ rnp->expmask &= ~mask;
+ __rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
+}
+
+/*
+ * Report expedited quiescent state for specified rcu_data (CPU).
+ */
+static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
+ bool wake)
+{
+ rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
+}
+
+/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
+static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,
+ unsigned long s)
+{
+ if (rcu_exp_gp_seq_done(rsp, s)) {
+ trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
+ /* Ensure test happens before caller kfree(). */
+ smp_mb__before_atomic(); /* ^^^ */
+ atomic_long_inc(stat);
+ return true;
+ }
+ return false;
+}
+
+/*
+ * Funnel-lock acquisition for expedited grace periods. Returns true
+ * if some other task completed an expedited grace period that this task
+ * can piggy-back on, and with no mutex held. Otherwise, returns false
+ * with the mutex held, indicating that the caller must actually do the
+ * expedited grace period.
+ */
+static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
+ struct rcu_node *rnp = rdp->mynode;
+ struct rcu_node *rnp_root = rcu_get_root(rsp);
+
+ /* Low-contention fastpath. */
+ if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
+ (rnp == rnp_root ||
+ ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
+ !mutex_is_locked(&rsp->exp_mutex) &&
+ mutex_trylock(&rsp->exp_mutex))
+ goto fastpath;
+
+ /*
+ * Each pass through the following loop works its way up
+ * the rcu_node tree, returning if others have done the work or
+ * otherwise falls through to acquire rsp->exp_mutex. The mapping
+ * from CPU to rcu_node structure can be inexact, as it is just
+ * promoting locality and is not strictly needed for correctness.
+ */
+ for (; rnp != NULL; rnp = rnp->parent) {
+ if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))
+ return true;
+
+ /* Work not done, either wait here or go up. */
+ spin_lock(&rnp->exp_lock);
+ if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
+
+ /* Someone else doing GP, so wait for them. */
+ spin_unlock(&rnp->exp_lock);
+ trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
+ rnp->grplo, rnp->grphi,
+ TPS("wait"));
+ wait_event(rnp->exp_wq[(s >> 1) & 0x3],
+ sync_exp_work_done(rsp,
+ &rdp->exp_workdone2, s));
+ return true;
+ }
+ rnp->exp_seq_rq = s; /* Followers can wait on us. */
+ spin_unlock(&rnp->exp_lock);
+ trace_rcu_exp_funnel_lock(rsp->name, rnp->level, rnp->grplo,
+ rnp->grphi, TPS("nxtlvl"));
+ }
+ mutex_lock(&rsp->exp_mutex);
+fastpath:
+ if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
+ mutex_unlock(&rsp->exp_mutex);
+ return true;
+ }
+ rcu_exp_gp_seq_start(rsp);
+ trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));
+ return false;
+}
+
+/* Invoked on each online non-idle CPU for expedited quiescent state. */
+static void sync_sched_exp_handler(void *data)
+{
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = data;
+
+ rdp = this_cpu_ptr(rsp->rda);
+ rnp = rdp->mynode;
+ if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
+ __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
+ return;
+ if (rcu_is_cpu_rrupt_from_idle()) {
+ rcu_report_exp_rdp(&rcu_sched_state,
+ this_cpu_ptr(&rcu_sched_data), true);
+ return;
+ }
+ __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
+ resched_cpu(smp_processor_id());
+}
+
+/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
+static void sync_sched_exp_online_cleanup(int cpu)
+{
+ struct rcu_data *rdp;
+ int ret;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = &rcu_sched_state;
+
+ rdp = per_cpu_ptr(rsp->rda, cpu);
+ rnp = rdp->mynode;
+ if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
+ return;
+ ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
+ WARN_ON_ONCE(ret);
+}
+
+/*
+ * Select the nodes that the upcoming expedited grace period needs
+ * to wait for.
+ */
+static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
+ smp_call_func_t func)
+{
+ int cpu;
+ unsigned long flags;
+ unsigned long mask;
+ unsigned long mask_ofl_test;
+ unsigned long mask_ofl_ipi;
+ int ret;
+ struct rcu_node *rnp;
+
+ sync_exp_reset_tree(rsp);
+ rcu_for_each_leaf_node(rsp, rnp) {
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+
+ /* Each pass checks a CPU for identity, offline, and idle. */
+ mask_ofl_test = 0;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+ struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+
+ if (raw_smp_processor_id() == cpu ||
+ !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
+ mask_ofl_test |= rdp->grpmask;
+ }
+ mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
+
+ /*
+ * Need to wait for any blocked tasks as well. Note that
+ * additional blocking tasks will also block the expedited
+ * GP until such time as the ->expmask bits are cleared.
+ */
+ if (rcu_preempt_has_tasks(rnp))
+ rnp->exp_tasks = rnp->blkd_tasks.next;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+ /* IPI the remaining CPUs for expedited quiescent state. */
+ mask = 1;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
+ if (!(mask_ofl_ipi & mask))
+ continue;
+retry_ipi:
+ ret = smp_call_function_single(cpu, func, rsp, 0);
+ if (!ret) {
+ mask_ofl_ipi &= ~mask;
+ continue;
+ }
+ /* Failed, raced with offline. */
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (cpu_online(cpu) &&
+ (rnp->expmask & mask)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ schedule_timeout_uninterruptible(1);
+ if (cpu_online(cpu) &&
+ (rnp->expmask & mask))
+ goto retry_ipi;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ }
+ if (!(rnp->expmask & mask))
+ mask_ofl_ipi &= ~mask;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
+ /* Report quiescent states for those that went offline. */
+ mask_ofl_test |= mask_ofl_ipi;
+ if (mask_ofl_test)
+ rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
+ }
+}
+
+static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
+{
+ int cpu;
+ unsigned long jiffies_stall;
+ unsigned long jiffies_start;
+ unsigned long mask;
+ int ndetected;
+ struct rcu_node *rnp;
+ struct rcu_node *rnp_root = rcu_get_root(rsp);
+ int ret;
+
+ jiffies_stall = rcu_jiffies_till_stall_check();
+ jiffies_start = jiffies;
+
+ for (;;) {
+ ret = swait_event_timeout(
+ rsp->expedited_wq,
+ sync_rcu_preempt_exp_done(rnp_root),
+ jiffies_stall);
+ if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
+ return;
+ if (ret < 0) {
+ /* Hit a signal, disable CPU stall warnings. */
+ swait_event(rsp->expedited_wq,
+ sync_rcu_preempt_exp_done(rnp_root));
+ return;
+ }
+ pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
+ rsp->name);
+ ndetected = 0;
+ rcu_for_each_leaf_node(rsp, rnp) {
+ ndetected += rcu_print_task_exp_stall(rnp);
+ mask = 1;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
+ struct rcu_data *rdp;
+
+ if (!(rnp->expmask & mask))
+ continue;
+ ndetected++;
+ rdp = per_cpu_ptr(rsp->rda, cpu);
+ pr_cont(" %d-%c%c%c", cpu,
+ "O."[!!cpu_online(cpu)],
+ "o."[!!(rdp->grpmask & rnp->expmaskinit)],
+ "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
+ }
+ mask <<= 1;
+ }
+ pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
+ jiffies - jiffies_start, rsp->expedited_sequence,
+ rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
+ if (ndetected) {
+ pr_err("blocking rcu_node structures:");
+ rcu_for_each_node_breadth_first(rsp, rnp) {
+ if (rnp == rnp_root)
+ continue; /* printed unconditionally */
+ if (sync_rcu_preempt_exp_done(rnp))
+ continue;
+ pr_cont(" l=%u:%d-%d:%#lx/%c",
+ rnp->level, rnp->grplo, rnp->grphi,
+ rnp->expmask,
+ ".T"[!!rnp->exp_tasks]);
+ }
+ pr_cont("\n");
+ }
+ rcu_for_each_leaf_node(rsp, rnp) {
+ mask = 1;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
+ if (!(rnp->expmask & mask))
+ continue;
+ dump_cpu_task(cpu);
+ }
+ }
+ jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
+ }
+}
+
+/*
+ * Wait for the current expedited grace period to complete, and then
+ * wake up everyone who piggybacked on the just-completed expedited
+ * grace period. Also update all the ->exp_seq_rq counters as needed
+ * in order to avoid counter-wrap problems.
+ */
+static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
+{
+ struct rcu_node *rnp;
+
+ synchronize_sched_expedited_wait(rsp);
+ rcu_exp_gp_seq_end(rsp);
+ trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));
+
+ /*
+ * Switch over to wakeup mode, allowing the next GP, but -only- the
+ * next GP, to proceed.
+ */
+ mutex_lock(&rsp->exp_wake_mutex);
+ mutex_unlock(&rsp->exp_mutex);
+
+ rcu_for_each_node_breadth_first(rsp, rnp) {
+ if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
+ spin_lock(&rnp->exp_lock);
+ /* Recheck, avoid hang in case someone just arrived. */
+ if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
+ rnp->exp_seq_rq = s;
+ spin_unlock(&rnp->exp_lock);
+ }
+ wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
+ }
+ trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
+ mutex_unlock(&rsp->exp_wake_mutex);
+}
+
+/**
+ * synchronize_sched_expedited - Brute-force RCU-sched grace period
+ *
+ * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
+ * approach to force the grace period to end quickly. This consumes
+ * significant time on all CPUs and is unfriendly to real-time workloads,
+ * so is thus not recommended for any sort of common-case code. In fact,
+ * if you are using synchronize_sched_expedited() in a loop, please
+ * restructure your code to batch your updates, and then use a single
+ * synchronize_sched() instead.
+ *
+ * This implementation can be thought of as an application of sequence
+ * locking to expedited grace periods, but using the sequence counter to
+ * determine when someone else has already done the work instead of for
+ * retrying readers.
+ */
+void synchronize_sched_expedited(void)
+{
+ unsigned long s;
+ struct rcu_state *rsp = &rcu_sched_state;
+
+ /* If only one CPU, this is automatically a grace period. */
+ if (rcu_blocking_is_gp())
+ return;
+
+ /* If expedited grace periods are prohibited, fall back to normal. */
+ if (rcu_gp_is_normal()) {
+ wait_rcu_gp(call_rcu_sched);
+ return;
+ }
+
+ /* Take a snapshot of the sequence number. */
+ s = rcu_exp_gp_seq_snap(rsp);
+ if (exp_funnel_lock(rsp, s))
+ return; /* Someone else did our work for us. */
+
+ /* Initialize the rcu_node tree in preparation for the wait. */
+ sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
+
+ /* Wait and clean up, including waking everyone. */
+ rcu_exp_wait_wake(rsp, s);
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
--
2.5.2
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