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Commit dddd3379 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
Browse files

perf: Fix inherit vs. context rotation bug 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Cc: <stable@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 02a9d037

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -850,6 +850,7 @@ struct perf_event_context { 
	int				nr_active;

	int				is_active;

	int				nr_stat;

	int				rotate_disable;

	atomic_t			refcount;

	struct task_struct		*task;

kernel/perf_event.c

+20 −2
Original line number Diff line number Diff line
@@ -1622,7 +1622,11 @@ static void rotate_ctx(struct perf_event_context *ctx) 
{

	raw_spin_lock(&ctx->lock);



	/* Rotate the first entry last of non-pinned 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);
@@ -6162,6 +6166,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn) 
	struct perf_event *event;

	struct task_struct *parent = current;

	int inherited_all = 1;

	unsigned long flags;

	int ret = 0;



	child->perf_event_ctxp[ctxn] = NULL;
@@ -6202,6 +6207,15 @@ int perf_event_init_context(struct task_struct *child, int ctxn) 
			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, ctxn, &inherited_all);
@@ -6209,6 +6223,10 @@ int perf_event_init_context(struct task_struct *child, int ctxn) 
			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[ctxn];



	if (child_ctx && inherited_all) {