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perf: Robustify event->owner usage and SMP ordering

Browse source 
Use smp_store_release() to clear event->owner and
lockless_dereference() to observe it. Further use READ_ONCE() for all
lockless reads.

This changes perf_remove_from_owner() to leave event->owner cleared.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra 2016-01-26 12:30:14 +01:00 • committed by Ingo Molnar
commit f47c02c0c8
1 changed files with 10 additions and 10 deletions
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20
kernel/events/core.c
View file

@ -152,7 +152,7 @@ static void perf_ctx_unlock(struct perf_cpu_context *cpuctx,
static bool is_kernel_event(struct perf_event *event)
{
return event->owner == TASK_TOMBSTONE;
return READ_ONCE(event->owner) == TASK_TOMBSTONE;
}
/*
@ -1651,7 +1651,7 @@ out:
*/
static bool is_orphaned_event(struct perf_event *event)
{
return event && !is_kernel_event(event) && !event->owner;
return event && !is_kernel_event(event) && !READ_ONCE(event->owner);
}
/*
@ -3733,14 +3733,13 @@ static void perf_remove_from_owner(struct perf_event *event)
struct task_struct *owner;
rcu_read_lock();
owner = ACCESS_ONCE(event->owner);
/*
* Matches the smp_wmb() in perf_event_exit_task(). If we observe
* !owner it means the list deletion is complete and we can indeed
* free this event, otherwise we need to serialize on
* Matches the smp_store_release() in perf_event_exit_task(). If we
* observe !owner it means the list deletion is complete and we can
* indeed free this event, otherwise we need to serialize on
* owner->perf_event_mutex.
*/
smp_read_barrier_depends();
owner = lockless_dereference(event->owner);
if (owner) {
/*
* Since delayed_put_task_struct() also drops the last
@ -3768,8 +3767,10 @@ static void perf_remove_from_owner(struct perf_event *event)
* ensured they're done, and we can proceed with freeing the
* event.
*/
if (event->owner)
if (event->owner) {
list_del_init(&event->owner_entry);
smp_store_release(&event->owner, NULL);
}
mutex_unlock(&owner->perf_event_mutex);
put_task_struct(owner);
}
@ -8829,8 +8830,7 @@ void perf_event_exit_task(struct task_struct *child)
* the owner, closes a race against perf_release() where
* we need to serialize on the owner->perf_event_mutex.
*/
smp_wmb();
event->owner = NULL;
smp_store_release(&event->owner, NULL);
}
mutex_unlock(&child->perf_event_mutex);