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>
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
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 @@
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)