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Commit 3f7cce3c authored by Stephane Eranian's avatar Stephane Eranian Committed by Ingo Molnar
Browse files

perf_events: Fix rcu and locking issues with cgroup support 



This patches ensures that we do not end up calling
perf_cgroup_from_task() when there is no cgroup event.
This avoids potential RCU and locking issues.

The change in perf_cgroup_set_timestamp() ensures we
check against ctx->nr_cgroups. It also avoids calling
perf_clock() tiwce in a row. It also ensures we do need
to grab ctx->lock before calling the function.

We drop update_cgrp_time() from task_clock_event_read()
because it is not needed. This also avoids having to
deal with perf_cgroup_from_task().

Thanks to Peter Zijlstra for his help on this.

Signed-off-by: default avatarStephane Eranian <eranian@gmail.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4d5e76b8.815bdf0a.7ac3.774f@mx.google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent c97cf422

kernel/perf_event.c

+29 −11
Original line number Diff line number Diff line
@@ -201,6 +201,11 @@ __get_cpu_context(struct perf_event_context *ctx) 


#ifdef CONFIG_CGROUP_PERF



/*

 * Must ensure cgroup is pinned (css_get) before calling

 * this function. In other words, we cannot call this function

 * if there is no cgroup event for the current CPU context.

 */

static inline struct perf_cgroup *

perf_cgroup_from_task(struct task_struct *task)

{
@@ -268,28 +273,41 @@ static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx) 


static inline void update_cgrp_time_from_event(struct perf_event *event)

{

	struct perf_cgroup *cgrp = perf_cgroup_from_task(current);

	struct perf_cgroup *cgrp;



	/*

	 * do not update time when cgroup is not active

	 * ensure we access cgroup data only when needed and

	 * when we know the cgroup is pinned (css_get)

	 */

	if (!event->cgrp || cgrp != event->cgrp)

	if (!is_cgroup_event(event))

		return;



	cgrp = perf_cgroup_from_task(current);

	/*

	 * Do not update time when cgroup is not active

	 */

	if (cgrp == event->cgrp)

		__update_cgrp_time(event->cgrp);

}



static inline void

perf_cgroup_set_timestamp(struct task_struct *task, u64 now)

perf_cgroup_set_timestamp(struct task_struct *task,

			  struct perf_event_context *ctx)

{

	struct perf_cgroup *cgrp;

	struct perf_cgroup_info *info;



	if (!task)

	/*

	 * ctx->lock held by caller

	 * ensure we do not access cgroup data

	 * unless we have the cgroup pinned (css_get)

	 */

	if (!task || !ctx->nr_cgroups)

		return;



	cgrp = perf_cgroup_from_task(task);

	info = this_cpu_ptr(cgrp->info);

	info->timestamp = now;

	info->timestamp = ctx->timestamp;

}



#define PERF_CGROUP_SWOUT	0x1 /* cgroup switch out every event */
@@ -494,7 +512,8 @@ static inline int perf_cgroup_connect(pid_t pid, struct perf_event *event, 
}



static inline void

perf_cgroup_set_timestamp(struct task_struct *task, u64 now)

perf_cgroup_set_timestamp(struct task_struct *task,

			  struct perf_event_context *ctx)

{

}
@@ -1613,7 +1632,7 @@ static int __perf_event_enable(void *info) 
	/*

	 * set current task's cgroup time reference point

	 */

	perf_cgroup_set_timestamp(current, perf_clock());

	perf_cgroup_set_timestamp(current, ctx);



	__perf_event_mark_enabled(event, ctx);
@@ -2048,7 +2067,7 @@ ctx_sched_in(struct perf_event_context *ctx, 


	now = perf_clock();

	ctx->timestamp = now;

	perf_cgroup_set_timestamp(task, now);

	perf_cgroup_set_timestamp(task, ctx);

	/*

	 * First go through the list and put on any pinned groups

	 * in order to give them the best chance of going on.
@@ -5795,7 +5814,6 @@ static void task_clock_event_read(struct perf_event *event) 


	if (!in_nmi()) {

		update_context_time(event->ctx);

		update_cgrp_time_from_event(event);

		time = event->ctx->time;

	} else {

		u64 now = perf_clock();