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perf_events: Fix rcu and locking issues with cgroup support

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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: Stephane Eranian <eranian@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4d5e76b8.815bdf0a.7ac3.774f@mx.google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Stephane Eranian 2011-02-18 14:40:01 +02:00 committed by Ingo Molnar
parent c97cf42219
commit 3f7cce3c18
1 changed files with 29 additions and 11 deletions
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40
kernel/perf_event.c
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@ -201,6 +201,11 @@ __get_cpu_context(struct perf_event_context *ctx)
#ifdef CONFIG_CGROUP_PERF #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 * static inline struct perf_cgroup *
perf_cgroup_from_task(struct task_struct *task) 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) 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; return;
__update_cgrp_time(event->cgrp); 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 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 *cgrp;
struct perf_cgroup_info *info; 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; return;
cgrp = perf_cgroup_from_task(task); cgrp = perf_cgroup_from_task(task);
info = this_cpu_ptr(cgrp->info); info = this_cpu_ptr(cgrp->info);
info->timestamp = now; info->timestamp = ctx->timestamp;
} }
#define PERF_CGROUP_SWOUT 0x1 /* cgroup switch out every event */ #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 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 * 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); __perf_event_mark_enabled(event, ctx);
@ -2048,7 +2067,7 @@ ctx_sched_in(struct perf_event_context *ctx,
now = perf_clock(); now = perf_clock();
ctx->timestamp = now; 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 * First go through the list and put on any pinned groups
* in order to give them the best chance of going on. * 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()) { if (!in_nmi()) {
update_context_time(event->ctx); update_context_time(event->ctx);
update_cgrp_time_from_event(event);
time = event->ctx->time; time = event->ctx->time;
} else { } else {
u64 now = perf_clock(); u64 now = perf_clock();