perf: Avoid race between cpu hotplug and installing event

perf_event_open() requires the cpu on which to install event is online,
but the cpu can go offline after perf_event_open checks that. Add a
get_online_cpus()/put_online_cpus() pair to avoid the race.

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1339741902-8449-3-git-send-email-zheng.z.yan@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d7d71d6ec972..31d182e01549 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6252,6 +6252,8 @@ SYSCALL_DEFINE5(perf_event_open,
                 }
         }
 
+        get_online_cpus();
+
         event = perf_event_alloc(&attr, cpu, task, group_leader, NULL,
                                  NULL, NULL);
         if (IS_ERR(event)) {
@@ -6391,6 +6393,8 @@ SYSCALL_DEFINE5(perf_event_open,
         perf_unpin_context(ctx);
         mutex_unlock(&ctx->mutex);
 
+        put_online_cpus();
+
         event->owner = current;
 
         mutex_lock(&current->perf_event_mutex);
@@ -6419,6 +6423,7 @@ err_context:
 err_alloc:
         free_event(event);
 err_task:
+        put_online_cpus();
         if (task)
                 put_task_struct(task);
 err_group_fd: