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Subject[tip:perf/urgent] perf_events: Fix stale ->cgrp pointer in update_cgrp_time_from_cpuctx()
Commit-ID:  68cacd29167b1926d237bd1b153aa2a990201729
Gitweb: http://git.kernel.org/tip/68cacd29167b1926d237bd1b153aa2a990201729
Author: Stephane Eranian <eranian@google.com>
AuthorDate: Wed, 23 Mar 2011 16:03:06 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 23 Mar 2011 16:07:22 +0100

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

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>
---
include/linux/perf_event.h | 2 --
kernel/perf_event.c | 12 +++++++++++-
2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f495c01..311b4dc 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -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 {
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 3472bb1..0c71422 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -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)

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