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Date: Tue, 9 Oct 2018 11:24:33 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: peterz@...radead.org, mingo@...hat.com
Cc: rostedt@...dmis.org, tglx@...utronix.de,
linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
alessio.balsini@...il.com, bristot@...hat.com, will.deacon@....com,
andrea.parri@...rulasolutions.com, dietmar.eggemann@....com,
patrick.bellasi@....com, henrik@...tad.us,
linux-rt-users@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>
Subject: [RFD/RFC PATCH 7/8] sched: Ensure blocked_on is always guarded by blocked_lock
blocked_on pointer might be concurrently modified by schedule() (when
proxy() is called) and by wakeup path, so we need to guard changes.
Ensure blocked_lock is always held before updating blocked_on pointer.
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
---
kernel/locking/mutex-debug.c | 1 +
kernel/locking/mutex.c | 13 ++++++++++---
kernel/sched/core.c | 31 ++++++++++++++++++++++++++++++-
3 files changed, 41 insertions(+), 4 deletions(-)
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index 6605e083a3e9..2e3fbdaa8474 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -62,6 +62,7 @@ void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
{
DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
DEBUG_LOCKS_WARN_ON(waiter->task != task);
+ DEBUG_LOCKS_WARN_ON(task->blocked_on == NULL);
DEBUG_LOCKS_WARN_ON(task->blocked_on != lock);
list_del_init(&waiter->list);
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index c16cb84420c3..8f6d4ceca2da 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -950,6 +950,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
}
raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ raw_spin_lock(¤t->blocked_lock);
/*
* After waiting to acquire the wait_lock, try again.
*/
@@ -1014,6 +1015,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
goto err;
}
+ raw_spin_unlock(¤t->blocked_lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
schedule_preempt_disabled();
@@ -1027,6 +1029,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
}
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ raw_spin_lock(¤t->blocked_lock);
/*
* Gets reset by ttwu_remote().
*/
@@ -1040,10 +1044,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
if (__mutex_trylock(lock) ||
(first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
break;
-
- raw_spin_lock_irqsave(&lock->wait_lock, flags);
}
- raw_spin_lock_irqsave(&lock->wait_lock, flags);
acquired:
__set_current_state(TASK_RUNNING);
@@ -1072,6 +1073,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
if (use_ww_ctx && ww_ctx)
ww_mutex_lock_acquired(ww, ww_ctx);
+ raw_spin_unlock(¤t->blocked_lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q);
preempt_enable();
@@ -1081,6 +1083,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
__set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, current);
err_early_kill:
+ raw_spin_unlock(¤t->blocked_lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, 1, ip);
@@ -1268,6 +1271,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
debug_mutex_unlock(lock);
#ifdef CONFIG_PROXY_EXEC
+ raw_spin_lock(¤t->blocked_lock);
/*
* If we have a task boosting us, and that task was boosting us through
* this lock, hand the lock that that task, as that is the highest
@@ -1305,6 +1309,9 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
__mutex_handoff(lock, next);
preempt_disable(); // XXX unlock->wakeup inversion like
+#ifdef CONFIG_PROXY_EXEC
+ raw_spin_unlock(¤t->blocked_lock);
+#endif
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q); // XXX must force resched on proxy
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e3e3eea3f5b2..54003515fd29 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1761,7 +1761,15 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
* trigger the on_rq_queued() clause for them.
*/
if (task_is_blocked(p)) {
- p->blocked_on = NULL; /* let it run again */
+ raw_spin_lock(&p->blocked_lock);
+
+ if (task_is_blocked(p)) {
+ p->blocked_on = NULL; /* let it run again */
+ } else {
+ raw_spin_unlock(&p->blocked_lock);
+ goto out_wakeup;
+ }
+
if (!cpumask_test_cpu(cpu_of(rq), &p->cpus_allowed)) {
/*
* proxy stuff moved us outside of the affinity mask
@@ -1771,6 +1779,7 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
p->on_rq = 0;
/* XXX [juril] SLEEP|NOCLOCK ? */
deactivate_task(rq, p, DEQUEUE_SLEEP);
+ raw_spin_unlock(&p->blocked_lock);
goto out_unlock;
}
@@ -1779,8 +1788,10 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
* executing context might not be the most elegible anymore.
*/
resched_curr(rq);
+ raw_spin_unlock(&p->blocked_lock);
}
+out_wakeup:
ttwu_do_wakeup(rq, p, wake_flags, &rf);
ret = 1;
@@ -3464,12 +3475,26 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
*/
for (p = next; p->blocked_on; p = owner) {
mutex = p->blocked_on;
+ if (!mutex)
+ return NULL;
/*
* By taking mutex->wait_lock we hold off concurrent mutex_unlock()
* and ensure @owner sticks around.
*/
raw_spin_lock(&mutex->wait_lock);
+ raw_spin_lock(&p->blocked_lock);
+
+ /* Check again that p is blocked with blocked_lock held */
+ if (task_is_blocked(p)) {
+ BUG_ON(mutex != p->blocked_on);
+ } else {
+ /* Something changed in the blocked_on chain */
+ raw_spin_unlock(&p->blocked_lock);
+ raw_spin_unlock(&mutex->wait_lock);
+ return NULL;
+ }
+
owner = __mutex_owner(mutex);
/*
* XXX can't this be 0|FLAGS? See __mutex_unlock_slowpath for(;;)
@@ -3491,6 +3516,7 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
* on this rq, therefore holding @rq->lock is sufficient to
* guarantee its existence, as per ttwu_remote().
*/
+ raw_spin_unlock(&p->blocked_lock);
raw_spin_unlock(&mutex->wait_lock);
owner->blocked_task = p;
@@ -3537,6 +3563,7 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
* @owner can disappear, simply migrate to @that_cpu and leave that CPU
* to sort things out.
*/
+ raw_spin_unlock(&p->blocked_lock);
raw_spin_unlock(&mutex->wait_lock);
/*
@@ -3661,6 +3688,7 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
* If @owner/@p is allowed to run on this CPU, make it go.
*/
if (cpumask_test_cpu(this_cpu, &owner->cpus_allowed)) {
+ raw_spin_unlock(&p->blocked_lock);
raw_spin_unlock(&mutex->wait_lock);
return owner;
}
@@ -3682,6 +3710,7 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
* We use @owner->blocked_lock to serialize against ttwu_activate().
* Either we see its new owner->on_rq or it will see our list_add().
*/
+ raw_spin_unlock(&p->blocked_lock);
raw_spin_lock(&owner->blocked_lock);
/*
--
2.17.1
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