lkml.org 
[lkml]   [2011]   [Feb]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Date
Subject[PATCH] 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: Stephane Eranian <eranian@gmail.com>
---

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index a0a6987..438d73a 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -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;

- __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
-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();

\
 
 \ /
  Last update: 2011-02-18 14:43    [W:0.053 / U:2.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site