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Subject[PATCH 3/4] scheduler: replace migration_thread with cpuhog
Date
Currently migration_thread is serving three purposes - migration
pusher, context to execute active_load_balance() and forced context
switcher for expedited RCU synchronize_sched. All three roles are
hardcoded into migration_thread() and determining which job is
scheduled is slightly messy.

This patch kills migration_thread and replaces all three uses with
cpuhog. The three different roles of migration_thread() are splitted
into three separate cpuhog callbacks - migration_hog(),
active_load_balance_hog() and synchronize_sched_expedited_hog() - and
each use case now simply asks cpuhog to execute the callback as
necessary.

synchronize_sched_expedited() was implemented with private
preallocated resources and custom multi-cpu queueing and waiting
logic, both of which are provided by cpuhog.
synchronize_sched_expedited_count is made atomic and all other shared
resources along with the mutex are dropped.

synchronize_sched_expedited() also implemented a check to detect cases
where not all the callback got executed on their assigned cpus and
fall back to synchronize_sched(). If called with cpu hotplug blocked,
cpuhog already guarantees that and the condition cannot happen;
otherwise, stop_machine() would break. However, this patch preserves
the paranoid check using a cpumask to record on which cpus the hog ran
so that it can serve as a bisection point if something actually goes
wrong theree.

Because the internal execution state is no longer visible,
rcu_expedited_torture_stats() is removed.

This patch also renames cpuhog threads to from "hog/%d" to
"migration/%d". The names of these threads ultimately don't matter
and there's no reason to make unnecessary userland visible changes.

With this patch applied, stop_machine() and sched now share the same
resources. stop_machine() is faster without wasting any resources and
sched migration users are much cleaner.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Josh Triplett <josh@freedesktop.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
---
Documentation/RCU/torture.txt | 10 --
include/linux/rcutiny.h | 2 -
include/linux/rcutree.h | 1 -
kernel/cpuhog.c | 2 +-
kernel/rcutorture.c | 2 +-
kernel/sched.c | 358 +++++++++++++----------------------------
6 files changed, 113 insertions(+), 262 deletions(-)
diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index 9dba3bb..c412018 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -170,16 +170,6 @@ Similarly, sched_expedited RCU provides the following:
sched_expedited-torture: Reader Pipe: 12660320201 95875 0 0 0 0 0 0 0 0 0
sched_expedited-torture: Reader Batch: 12660424885 0 0 0 0 0 0 0 0 0 0
sched_expedited-torture: Free-Block Circulation: 1090795 1090795 1090794 1090793 1090792 1090791 1090790 1090789 1090788 1090787 0
- state: -1 / 0:0 3:0 4:0
-
-As before, the first four lines are similar to those for RCU.
-The last line shows the task-migration state. The first number is
--1 if synchronize_sched_expedited() is idle, -2 if in the process of
-posting wakeups to the migration kthreads, and N when waiting on CPU N.
-Each of the colon-separated fields following the "/" is a CPU:state pair.
-Valid states are "0" for idle, "1" for waiting for quiescent state,
-"2" for passed through quiescent state, and "3" when a race with a
-CPU-hotplug event forces use of the synchronize_sched() primitive.


USAGE
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 96cc307..49d3d46 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -60,8 +60,6 @@ static inline long rcu_batches_completed_bh(void)
return 0;
}

-extern int rcu_expedited_torture_stats(char *page);
-
#define synchronize_rcu synchronize_sched

static inline void synchronize_rcu_expedited(void)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 8044b1b..65e0740 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -36,7 +36,6 @@ extern void rcu_sched_qs(int cpu);
extern void rcu_bh_qs(int cpu);
extern int rcu_needs_cpu(int cpu);
extern void rcu_scheduler_starting(void);
-extern int rcu_expedited_torture_stats(char *page);

#ifdef CONFIG_TREE_PREEMPT_RCU

diff --git a/kernel/cpuhog.c b/kernel/cpuhog.c
index c25c510..353a157 100644
--- a/kernel/cpuhog.c
+++ b/kernel/cpuhog.c
@@ -289,7 +289,7 @@ static int __cpuinit cpuhog_cpu_callback(struct notifier_block *nfb,
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_UP_PREPARE:
BUG_ON(hog->thread || hog->enabled || !list_empty(&hog->works));
- p = kthread_create(cpuhog_thread, hog, "hog/%d", cpu);
+ p = kthread_create(cpuhog_thread, hog, "migration/%d", cpu);
if (IS_ERR(p))
return NOTIFY_BAD;
sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 9bb5217..57f61b5 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -650,7 +650,7 @@ static struct rcu_torture_ops sched_expedited_ops = {
.deferred_free = rcu_sync_torture_deferred_free,
.sync = synchronize_sched_expedited,
.cb_barrier = NULL,
- .stats = rcu_expedited_torture_stats,
+ .stats = NULL,
.irq_capable = 1,
.name = "sched_expedited"
};
diff --git a/kernel/sched.c b/kernel/sched.c
index 3a8fb30..900088d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -53,9 +53,9 @@
#include <linux/timer.h>
#include <linux/rcupdate.h>
#include <linux/cpu.h>
+#include <linux/cpuhog.h>
#include <linux/cpuset.h>
#include <linux/percpu.h>
-#include <linux/kthread.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/sysctl.h>
@@ -578,15 +578,13 @@ struct rq {
int post_schedule;
int active_balance;
int push_cpu;
+ struct cpuhog_work active_balance_work;
/* cpu of this runqueue: */
int cpu;
int online;

unsigned long avg_load_per_task;

- struct task_struct *migration_thread;
- struct list_head migration_queue;
-
u64 rt_avg;
u64 age_stamp;
u64 idle_stamp;
@@ -2053,21 +2051,18 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
__set_task_cpu(p, new_cpu);
}

-struct migration_req {
- struct list_head list;
-
+struct migration_arg {
struct task_struct *task;
int dest_cpu;
-
- struct completion done;
};

+static int migration_hog(void *data);
+
/*
* The task's runqueue lock must be held.
* Returns true if you have to wait for migration thread.
*/
-static int
-migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
+static bool migrate_task(struct task_struct *p, int dest_cpu)
{
struct rq *rq = task_rq(p);

@@ -2075,15 +2070,7 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
* If the task is not on a runqueue (and not running), then
* the next wake-up will properly place the task.
*/
- if (!p->se.on_rq && !task_running(rq, p))
- return 0;
-
- init_completion(&req->done);
- req->task = p;
- req->dest_cpu = dest_cpu;
- list_add(&req->list, &rq->migration_queue);
-
- return 1;
+ return p->se.on_rq || task_running(rq, p);
}

/*
@@ -3149,7 +3136,6 @@ static void double_rq_unlock(struct rq *rq1, struct rq *rq2)
void sched_exec(void)
{
struct task_struct *p = current;
- struct migration_req req;
int dest_cpu, this_cpu;
unsigned long flags;
struct rq *rq;
@@ -3175,16 +3161,11 @@ again:
}

/* force the process onto the specified CPU */
- if (migrate_task(p, dest_cpu, &req)) {
- /* Need to wait for migration thread (might exit: take ref). */
- struct task_struct *mt = rq->migration_thread;
+ if (migrate_task(p, dest_cpu)) {
+ struct migration_arg arg = { p, dest_cpu };

- get_task_struct(mt);
task_rq_unlock(rq, &flags);
- wake_up_process(mt);
- put_task_struct(mt);
- wait_for_completion(&req.done);
-
+ hog_one_cpu(this_cpu, migration_hog, &arg);
return;
}
task_rq_unlock(rq, &flags);
@@ -4143,6 +4124,8 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
/* Working cpumask for load_balance and load_balance_newidle. */
static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);

+static int active_load_balance_hog(void *data);
+
/*
* Check this_cpu to ensure it is balanced within domain. Attempt to move
* tasks if there is an imbalance.
@@ -4233,7 +4216,7 @@ redo:

raw_spin_lock_irqsave(&busiest->lock, flags);

- /* don't kick the migration_thread, if the curr
+ /* don't kick the active_load_balance_hog, if the curr
* task on busiest cpu can't be moved to this_cpu
*/
if (!cpumask_test_cpu(this_cpu,
@@ -4251,7 +4234,9 @@ redo:
}
raw_spin_unlock_irqrestore(&busiest->lock, flags);
if (active_balance)
- wake_up_process(busiest->migration_thread);
+ hog_one_cpu_nowait(cpu_of(busiest),
+ active_load_balance_hog, busiest,
+ &busiest->active_balance_work);

/*
* We've kicked active balancing, reset the failure
@@ -4412,7 +4397,7 @@ redo:
double_lock_balance(this_rq, busiest);

/*
- * don't kick the migration_thread, if the curr
+ * don't kick the active_load_balance_hog, if the curr
* task on busiest cpu can't be moved to this_cpu
*/
if (!cpumask_test_cpu(this_cpu, &busiest->curr->cpus_allowed)) {
@@ -4433,7 +4418,9 @@ redo:
*/
raw_spin_unlock(&this_rq->lock);
if (active_balance)
- wake_up_process(busiest->migration_thread);
+ hog_one_cpu_nowait(cpu_of(busiest),
+ active_load_balance_hog, busiest,
+ &busiest->active_balance_work);
raw_spin_lock(&this_rq->lock);

} else
@@ -4496,24 +4483,29 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
}

/*
- * active_load_balance is run by migration threads. It pushes running tasks
- * off the busiest CPU onto idle CPUs. It requires at least 1 task to be
- * running on each physical CPU where possible, and avoids physical /
- * logical imbalances.
- *
- * Called with busiest_rq locked.
+ * active_load_balance_hog is run by cpuhog. It pushes running tasks
+ * off the busiest CPU onto idle CPUs. It requires at least 1 task to
+ * be running on each physical CPU where possible, and avoids physical
+ * / logical imbalances.
*/
-static void active_load_balance(struct rq *busiest_rq, int busiest_cpu)
+static int active_load_balance_hog(void *data)
{
+ struct rq *busiest_rq = data;
+ int busiest_cpu = cpu_of(busiest_rq);
int target_cpu = busiest_rq->push_cpu;
+ struct rq *target_rq = cpu_rq(target_cpu);
struct sched_domain *sd;
- struct rq *target_rq;
+
+ raw_spin_lock_irq(&busiest_rq->lock);
+
+ /* make sure the requested cpu hasn't gone down in the meantime */
+ if (unlikely(busiest_cpu != smp_processor_id() ||
+ !busiest_rq->active_balance))
+ goto out_unlock;

/* Is there any task to move? */
if (busiest_rq->nr_running <= 1)
- return;
-
- target_rq = cpu_rq(target_cpu);
+ goto out_unlock;

/*
* This condition is "impossible", if it occurs
@@ -4544,6 +4536,10 @@ static void active_load_balance(struct rq *busiest_rq, int busiest_cpu)
schedstat_inc(sd, alb_failed);
}
double_unlock_balance(busiest_rq, target_rq);
+out_unlock:
+ busiest_rq->active_balance = 0;
+ raw_spin_unlock_irq(&busiest_rq->lock);
+ return 0;
}

#ifdef CONFIG_NO_HZ
@@ -7116,17 +7112,12 @@ static inline void sched_init_granularity(void)
/*
* This is how migration works:
*
- * 1) we queue a struct migration_req structure in the source CPU's
- * runqueue and wake up that CPU's migration thread.
- * 2) we down() the locked semaphore => thread blocks.
- * 3) migration thread wakes up (implicitly it forces the migrated
- * thread off the CPU)
- * 4) it gets the migration request and checks whether the migrated
- * task is still in the wrong runqueue.
- * 5) if it's in the wrong runqueue then the migration thread removes
+ * 1) we invoke migration_hog() on the target CPU using hog_one_cpu().
+ * 2) hog starts to run (implicitly forcing the migrated thread off the CPU)
+ * 3) it checks whether the migrated task is still in the wrong runqueue.
+ * 4) if it's in the wrong runqueue then the migration thread removes
* it and puts it into the right queue.
- * 6) migration thread up()s the semaphore.
- * 7) we wake up and the migration is done.
+ * 5) hog completes and hog_one_cpu() returns and the migration is done.
*/

/*
@@ -7140,9 +7131,9 @@ static inline void sched_init_granularity(void)
*/
int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
{
- struct migration_req req;
unsigned long flags;
struct rq *rq;
+ unsigned int dest_cpu;
int ret = 0;

/*
@@ -7188,15 +7179,12 @@ again:
if (cpumask_test_cpu(task_cpu(p), new_mask))
goto out;

- if (migrate_task(p, cpumask_any_and(cpu_active_mask, new_mask), &req)) {
+ dest_cpu = cpumask_any_and(cpu_active_mask, new_mask);
+ if (migrate_task(p, dest_cpu)) {
+ struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */
- struct task_struct *mt = rq->migration_thread;
-
- get_task_struct(mt);
task_rq_unlock(rq, &flags);
- wake_up_process(rq->migration_thread);
- put_task_struct(mt);
- wait_for_completion(&req.done);
+ hog_one_cpu(cpu_of(rq), migration_hog, &arg);
tlb_migrate_finish(p->mm);
return 0;
}
@@ -7254,75 +7242,6 @@ fail:
return ret;
}

-#define RCU_MIGRATION_IDLE 0
-#define RCU_MIGRATION_NEED_QS 1
-#define RCU_MIGRATION_GOT_QS 2
-#define RCU_MIGRATION_MUST_SYNC 3
-
-/*
- * migration_thread - this is a highprio system thread that performs
- * thread migration by bumping thread off CPU then 'pushing' onto
- * another runqueue.
- */
-static int migration_thread(void *data)
-{
- int badcpu;
- int cpu = (long)data;
- struct rq *rq;
-
- rq = cpu_rq(cpu);
- BUG_ON(rq->migration_thread != current);
-
- set_current_state(TASK_INTERRUPTIBLE);
- while (!kthread_should_stop()) {
- struct migration_req *req;
- struct list_head *head;
-
- raw_spin_lock_irq(&rq->lock);
-
- if (cpu_is_offline(cpu)) {
- raw_spin_unlock_irq(&rq->lock);
- break;
- }
-
- if (rq->active_balance) {
- active_load_balance(rq, cpu);
- rq->active_balance = 0;
- }
-
- head = &rq->migration_queue;
-
- if (list_empty(head)) {
- raw_spin_unlock_irq(&rq->lock);
- schedule();
- set_current_state(TASK_INTERRUPTIBLE);
- continue;
- }
- req = list_entry(head->next, struct migration_req, list);
- list_del_init(head->next);
-
- if (req->task != NULL) {
- raw_spin_unlock(&rq->lock);
- __migrate_task(req->task, cpu, req->dest_cpu);
- } else if (likely(cpu == (badcpu = smp_processor_id()))) {
- req->dest_cpu = RCU_MIGRATION_GOT_QS;
- raw_spin_unlock(&rq->lock);
- } else {
- req->dest_cpu = RCU_MIGRATION_MUST_SYNC;
- raw_spin_unlock(&rq->lock);
- WARN_ONCE(1, "migration_thread() on CPU %d, expected %d\n", badcpu, cpu);
- }
- local_irq_enable();
-
- complete(&req->done);
- }
- __set_current_state(TASK_RUNNING);
-
- return 0;
-}
-
-#ifdef CONFIG_HOTPLUG_CPU
-
static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu)
{
int ret;
@@ -7334,6 +7253,25 @@ static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu)
}

/*
+ * migration_hog - this will be executed by a highprio cpuhog thread
+ * and performs thread migration by bumping thread off CPU then
+ * 'pushing' onto another runqueue.
+ */
+static int migration_hog(void *data)
+{
+ struct migration_arg *arg = data;
+
+ /*
+ * The original target cpu might have gone down and we might
+ * be on another cpu but it doesn't matter.
+ */
+ __migrate_task_irq(arg->task, raw_smp_processor_id(), arg->dest_cpu);
+ return 0;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
* Figure out where task on dead CPU should go, use force if necessary.
*/
static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)
@@ -7687,35 +7625,20 @@ static void set_rq_offline(struct rq *rq)
static int __cpuinit
migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
{
- struct task_struct *p;
int cpu = (long)hcpu;
unsigned long flags;
- struct rq *rq;
+ struct rq *rq = cpu_rq(cpu);

switch (action) {

case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
- p = kthread_create(migration_thread, hcpu, "migration/%d", cpu);
- if (IS_ERR(p))
- return NOTIFY_BAD;
- kthread_bind(p, cpu);
- /* Must be high prio: stop_machine expects to yield to it. */
- rq = task_rq_lock(p, &flags);
- __setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
- task_rq_unlock(rq, &flags);
- get_task_struct(p);
- cpu_rq(cpu)->migration_thread = p;
rq->calc_load_update = calc_load_update;
break;

case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
- /* Strictly unnecessary, as first user will wake it. */
- wake_up_process(cpu_rq(cpu)->migration_thread);
-
/* Update our root-domain */
- rq = cpu_rq(cpu);
raw_spin_lock_irqsave(&rq->lock, flags);
if (rq->rd) {
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
@@ -7726,26 +7649,10 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
break;

#ifdef CONFIG_HOTPLUG_CPU
- case CPU_UP_CANCELED:
- case CPU_UP_CANCELED_FROZEN:
- if (!cpu_rq(cpu)->migration_thread)
- break;
- /* Unbind it from offline cpu so it can run. Fall thru. */
- kthread_bind(cpu_rq(cpu)->migration_thread,
- cpumask_any(cpu_online_mask));
- kthread_stop(cpu_rq(cpu)->migration_thread);
- put_task_struct(cpu_rq(cpu)->migration_thread);
- cpu_rq(cpu)->migration_thread = NULL;
- break;
-
case CPU_DEAD:
case CPU_DEAD_FROZEN:
cpuset_lock(); /* around calls to cpuset_cpus_allowed_lock() */
migrate_live_tasks(cpu);
- rq = cpu_rq(cpu);
- kthread_stop(rq->migration_thread);
- put_task_struct(rq->migration_thread);
- rq->migration_thread = NULL;
/* Idle task back to normal (off runqueue, low prio) */
raw_spin_lock_irq(&rq->lock);
update_rq_clock(rq);
@@ -7758,29 +7665,11 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
migrate_nr_uninterruptible(rq);
BUG_ON(rq->nr_running != 0);
calc_global_load_remove(rq);
- /*
- * No need to migrate the tasks: it was best-effort if
- * they didn't take sched_hotcpu_mutex. Just wake up
- * the requestors.
- */
- raw_spin_lock_irq(&rq->lock);
- while (!list_empty(&rq->migration_queue)) {
- struct migration_req *req;
-
- req = list_entry(rq->migration_queue.next,
- struct migration_req, list);
- list_del_init(&req->list);
- raw_spin_unlock_irq(&rq->lock);
- complete(&req->done);
- raw_spin_lock_irq(&rq->lock);
- }
- raw_spin_unlock_irq(&rq->lock);
break;

case CPU_DYING:
case CPU_DYING_FROZEN:
/* Update our root-domain */
- rq = cpu_rq(cpu);
raw_spin_lock_irqsave(&rq->lock, flags);
if (rq->rd) {
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
@@ -9642,10 +9531,8 @@ void __init sched_init(void)
rq->push_cpu = 0;
rq->cpu = i;
rq->online = 0;
- rq->migration_thread = NULL;
rq->idle_stamp = 0;
rq->avg_idle = 2*sysctl_sched_migration_cost;
- INIT_LIST_HEAD(&rq->migration_queue);
rq_attach_root(rq, &def_root_domain);
#endif
init_rq_hrtick(rq);
@@ -10931,12 +10818,6 @@ struct cgroup_subsys cpuacct_subsys = {

#ifndef CONFIG_SMP

-int rcu_expedited_torture_stats(char *page)
-{
- return 0;
-}
-EXPORT_SYMBOL_GPL(rcu_expedited_torture_stats);
-
void synchronize_sched_expedited(void)
{
}
@@ -10944,30 +10825,20 @@ EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

#else /* #ifndef CONFIG_SMP */

-static DEFINE_PER_CPU(struct migration_req, rcu_migration_req);
-static DEFINE_MUTEX(rcu_sched_expedited_mutex);
-
-#define RCU_EXPEDITED_STATE_POST -2
-#define RCU_EXPEDITED_STATE_IDLE -1
-
-static int rcu_expedited_state = RCU_EXPEDITED_STATE_IDLE;
+static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0);

-int rcu_expedited_torture_stats(char *page)
+static int synchronize_sched_expedited_hog(void *data)
{
- int cnt = 0;
- int cpu;
+ static DEFINE_SPINLOCK(done_mask_lock);
+ struct cpumask *done_mask = data;

- cnt += sprintf(&page[cnt], "state: %d /", rcu_expedited_state);
- for_each_online_cpu(cpu) {
- cnt += sprintf(&page[cnt], " %d:%d",
- cpu, per_cpu(rcu_migration_req, cpu).dest_cpu);
+ if (done_mask) {
+ spin_lock(&done_mask_lock);
+ cpumask_set_cpu(smp_processor_id(), done_mask);
+ spin_unlock(&done_mask_lock);
}
- cnt += sprintf(&page[cnt], "\n");
- return cnt;
+ return 0;
}
-EXPORT_SYMBOL_GPL(rcu_expedited_torture_stats);
-
-static long synchronize_sched_expedited_count;

/*
* Wait for an rcu-sched grace period to elapse, but use "big hammer"
@@ -10981,60 +10852,53 @@ static long synchronize_sched_expedited_count;
*/
void synchronize_sched_expedited(void)
{
- int cpu;
- unsigned long flags;
- bool need_full_sync = 0;
- struct rq *rq;
- struct migration_req *req;
- long snap;
- int trycount = 0;
+ cpumask_var_t done_mask_var;
+ struct cpumask *done_mask = NULL;
+ int snap, trycount = 0;
+
+ /*
+ * done_mask is used to check that all cpus actually have
+ * finished running the hog, which is guaranteed by hog_cpus()
+ * if it's called with cpu hotplug blocked. Keep the paranoia
+ * for now but it's best effort if cpumask is off stack.
+ */
+ if (zalloc_cpumask_var(&done_mask_var, GFP_ATOMIC))
+ done_mask = done_mask_var;

smp_mb(); /* ensure prior mod happens before capturing snap. */
- snap = ACCESS_ONCE(synchronize_sched_expedited_count) + 1;
+ snap = atomic_read(&synchronize_sched_expedited_count) + 1;
get_online_cpus();
- while (!mutex_trylock(&rcu_sched_expedited_mutex)) {
+ while (try_hog_cpus(cpu_online_mask, synchronize_sched_expedited_hog,
+ done_mask) == -EAGAIN) {
put_online_cpus();
if (trycount++ < 10)
udelay(trycount * num_online_cpus());
else {
synchronize_sched();
- return;
+ goto free_out;
}
- if (ACCESS_ONCE(synchronize_sched_expedited_count) - snap > 0) {
+ if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) {
smp_mb(); /* ensure test happens before caller kfree */
- return;
+ goto free_out;
}
get_online_cpus();
}
- rcu_expedited_state = RCU_EXPEDITED_STATE_POST;
- for_each_online_cpu(cpu) {
- rq = cpu_rq(cpu);
- req = &per_cpu(rcu_migration_req, cpu);
- init_completion(&req->done);
- req->task = NULL;
- req->dest_cpu = RCU_MIGRATION_NEED_QS;
- raw_spin_lock_irqsave(&rq->lock, flags);
- list_add(&req->list, &rq->migration_queue);
- raw_spin_unlock_irqrestore(&rq->lock, flags);
- wake_up_process(rq->migration_thread);
- }
- for_each_online_cpu(cpu) {
- rcu_expedited_state = cpu;
- req = &per_cpu(rcu_migration_req, cpu);
- rq = cpu_rq(cpu);
- wait_for_completion(&req->done);
- raw_spin_lock_irqsave(&rq->lock, flags);
- if (unlikely(req->dest_cpu == RCU_MIGRATION_MUST_SYNC))
- need_full_sync = 1;
- req->dest_cpu = RCU_MIGRATION_IDLE;
- raw_spin_unlock_irqrestore(&rq->lock, flags);
- }
- rcu_expedited_state = RCU_EXPEDITED_STATE_IDLE;
- synchronize_sched_expedited_count++;
- mutex_unlock(&rcu_sched_expedited_mutex);
+ atomic_inc(&synchronize_sched_expedited_count);
+ if (done_mask)
+ cpumask_xor(done_mask, done_mask, cpu_online_mask);
put_online_cpus();
- if (need_full_sync)
+
+ /* paranoia - this can't happen */
+ if (done_mask && cpumask_weight(done_mask)) {
+ char buf[80];
+
+ cpulist_scnprintf(buf, sizeof(buf), done_mask);
+ WARN_ONCE(1, "synchronize_sched_expedited: cpu online and done masks disagree on %d cpus: %s\n",
+ cpumask_weight(done_mask), buf);
synchronize_sched();
+ }
+free_out:
+ free_cpumask_var(done_mask_var);
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

--
1.6.4.2


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