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perf: Fix inherit vs. context rotation bug

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commit dddd3379a6 upstream.

It was found that sometimes children of tasks with inherited events had
one extra event. Eventually it turned out to be due to the list rotation
no being exclusive with the list iteration in the inheritance code.

Cure this by temporarily disabling the rotation while we inherit the events.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Thomas Gleixner 2010-11-24 10:05:55 +01:00 committed by Greg Kroah-Hartman
parent fc359f622b
commit 03aff981d0
2 changed files with 21 additions and 2 deletions
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1
include/linux/perf_event.h
View File

@ -788,6 +788,7 @@ struct perf_event_context {
int nr_active;
int is_active;
int nr_stat;
int rotate_disable;
atomic_t refcount;
struct task_struct *task;

22
kernel/perf_event.c
View File

@ -1620,8 +1620,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
{
raw_spin_lock(&ctx->lock);
/* Rotate the first entry last of non-pinned groups */
list_rotate_left(&ctx->flexible_groups);
/*
* Rotate the first entry last of non-pinned groups. Rotation might be
* disabled by the inheritance code.
*/
if (!ctx->rotate_disable)
list_rotate_left(&ctx->flexible_groups);
raw_spin_unlock(&ctx->lock);
}
@ -5622,6 +5626,7 @@ int perf_event_init_task(struct task_struct *child)
struct perf_event *event;
struct task_struct *parent = current;
int inherited_all = 1;
unsigned long flags;
int ret = 0;
child->perf_event_ctxp = NULL;
@ -5662,6 +5667,15 @@ int perf_event_init_task(struct task_struct *child)
break;
}
/*
* We can't hold ctx->lock when iterating the ->flexible_group list due
* to allocations, but we need to prevent rotation because
* rotate_ctx() will change the list from interrupt context.
*/
raw_spin_lock_irqsave(&parent_ctx->lock, flags);
parent_ctx->rotate_disable = 1;
raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
ret = inherit_task_group(event, parent, parent_ctx, child,
&inherited_all);
@ -5669,6 +5683,10 @@ int perf_event_init_task(struct task_struct *child)
break;
}
raw_spin_lock_irqsave(&parent_ctx->lock, flags);
parent_ctx->rotate_disable = 0;
raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
child_ctx = child->perf_event_ctxp;
if (child_ctx && inherited_all) {