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perf_events: Fix stale ->cgrp pointer in update_cgrp_time_from_cpuctx()

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This patch solves a stale pointer problem in
update_cgrp_time_from_cpuctx(). The cpuctx->cgrp
was not cleared on all possible event exit paths,
including:

   close()
     perf_release()
       perf_release_kernel()
         list_del_event()

This patch fixes list_del_event() to clear cpuctx->cgrp
when there are no cgroup events left in the context.

[ This second version makes the code compile when
  CONFIG_CGROUP_PERF is not enabled. We unconditionally define
  perf_cpu_context->cgrp. ]

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: peterz@infradead.org
Cc: perfmon2-devel@lists.sf.net
Cc: paulus@samba.org
Cc: davem@davemloft.net
LKML-Reference: <20110323150306.GA1580@quad>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Stephane Eranian 2011-03-23 16:03:06 +01:00 committed by Ingo Molnar
parent ce2d17ca7f
commit 68cacd2916
2 changed files with 11 additions and 3 deletions
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2
include/linux/perf_event.h
View File

@ -938,9 +938,7 @@ struct perf_cpu_context {
struct list_head rotation_list;
int jiffies_interval;
struct pmu *active_pmu;
#ifdef CONFIG_CGROUP_PERF
struct perf_cgroup *cgrp;
#endif
};
struct perf_output_handle {

12
kernel/perf_event.c
View File

@ -941,6 +941,7 @@ static void perf_group_attach(struct perf_event *event)
static void
list_del_event(struct perf_event *event, struct perf_event_context *ctx)
{
struct perf_cpu_context *cpuctx;
/*
* We can have double detach due to exit/hot-unplug + close.
*/
@ -949,8 +950,17 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
event->attach_state &= ~PERF_ATTACH_CONTEXT;
if (is_cgroup_event(event))
if (is_cgroup_event(event)) {
ctx->nr_cgroups--;
cpuctx = __get_cpu_context(ctx);
/*
* if there are no more cgroup events
* then cler cgrp to avoid stale pointer
* in update_cgrp_time_from_cpuctx()
*/
if (!ctx->nr_cgroups)
cpuctx->cgrp = NULL;
}
ctx->nr_events--;
if (event->attr.inherit_stat)