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authorPeter Zijlstra <peterz@infradead.org>2016-02-24 17:45:44 (GMT)
committerIngo Molnar <mingo@kernel.org>2016-02-25 07:42:33 (GMT)
commita69b0ca4ac3bf5427b571f11cbf33f0a32b728d5 (patch)
tree551099312337a9f3a435f1169d857385972d48b3 /kernel
parent6f932e5be1503ab0783699e843db325d44c2fabb (diff)
downloadlinux-a69b0ca4ac3bf5427b571f11cbf33f0a32b728d5.tar.xz
perf: Fix cloning
Alexander reported that when the 'original' context gets destroyed, no new clones happen. This can happen irrespective of the ctx switch optimization, any task can die, even the parent, and we want to continue monitoring the task hierarchy until we either close the event or no tasks are left in the hierarchy. perf_event_init_context() will attempt to pin the 'parent' context during clone(). At that point current is the parent, and since current cannot have exited while executing clone(), its context cannot have passed through perf_event_exit_task_context(). Therefore perf_pin_task_context() cannot observe ctx->task == TASK_TOMBSTONE. However, since inherit_event() does: if (parent_event->parent) parent_event = parent_event->parent; it looks at the 'original' event when it does: is_orphaned_event(). This can return true if the context that contains the this event has passed through perf_event_exit_task_context(). And thus we'll fail to clone the perf context. Fix this by adding a new state: STATE_DEAD, which is set by perf_release() to indicate that the filedesc (or kernel reference) is dead and there are no observers for our data left. Only for STATE_DEAD will is_orphaned_event() be true and inhibit cloning. STATE_EXIT is otherwise preserved such that is_event_hup() remains functional and will report when the observed task hierarchy becomes empty. Reported-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dvyukov@google.com Cc: eranian@google.com Cc: oleg@redhat.com Cc: panand@redhat.com Cc: sasha.levin@oracle.com Cc: vince@deater.net Fixes: c6e5b73242d2 ("perf: Synchronously clean up child events") Link: http://lkml.kernel.org/r/20160224174947.919845295@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/events/core.c29
1 files changed, 14 insertions, 15 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 64698fb..92d6999 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1645,7 +1645,7 @@ out:
static bool is_orphaned_event(struct perf_event *event)
{
- return event->state == PERF_EVENT_STATE_EXIT;
+ return event->state == PERF_EVENT_STATE_DEAD;
}
static inline int pmu_filter_match(struct perf_event *event)
@@ -1732,7 +1732,6 @@ group_sched_out(struct perf_event *group_event,
}
#define DETACH_GROUP 0x01UL
-#define DETACH_STATE 0x02UL
/*
* Cross CPU call to remove a performance event
@@ -1752,8 +1751,6 @@ __perf_remove_from_context(struct perf_event *event,
if (flags & DETACH_GROUP)
perf_group_detach(event);
list_del_event(event, ctx);
- if (flags & DETACH_STATE)
- event->state = PERF_EVENT_STATE_EXIT;
if (!ctx->nr_events && ctx->is_active) {
ctx->is_active = 0;
@@ -3772,22 +3769,24 @@ int perf_event_release_kernel(struct perf_event *event)
ctx = perf_event_ctx_lock(event);
WARN_ON_ONCE(ctx->parent_ctx);
- perf_remove_from_context(event, DETACH_GROUP | DETACH_STATE);
- perf_event_ctx_unlock(event, ctx);
+ perf_remove_from_context(event, DETACH_GROUP);
+ raw_spin_lock_irq(&ctx->lock);
/*
- * At this point we must have event->state == PERF_EVENT_STATE_EXIT,
- * either from the above perf_remove_from_context() or through
- * perf_event_exit_event().
+ * Mark this even as STATE_DEAD, there is no external reference to it
+ * anymore.
*
- * Therefore, anybody acquiring event->child_mutex after the below
- * loop _must_ also see this, most importantly inherit_event() which
- * will avoid placing more children on the list.
+ * Anybody acquiring event->child_mutex after the below loop _must_
+ * also see this, most importantly inherit_event() which will avoid
+ * placing more children on the list.
*
* Thus this guarantees that we will in fact observe and kill _ALL_
* child events.
*/
- WARN_ON_ONCE(event->state != PERF_EVENT_STATE_EXIT);
+ event->state = PERF_EVENT_STATE_DEAD;
+ raw_spin_unlock_irq(&ctx->lock);
+
+ perf_event_ctx_unlock(event, ctx);
again:
mutex_lock(&event->child_mutex);
@@ -4000,7 +3999,7 @@ static bool is_event_hup(struct perf_event *event)
{
bool no_children;
- if (event->state != PERF_EVENT_STATE_EXIT)
+ if (event->state > PERF_EVENT_STATE_EXIT)
return false;
mutex_lock(&event->child_mutex);
@@ -8727,7 +8726,7 @@ perf_event_exit_event(struct perf_event *child_event,
if (parent_event)
perf_group_detach(child_event);
list_del_event(child_event, child_ctx);
- child_event->state = PERF_EVENT_STATE_EXIT; /* see perf_event_release_kernel() */
+ child_event->state = PERF_EVENT_STATE_EXIT; /* is_event_hup() */
raw_spin_unlock_irq(&child_ctx->lock);
/*