perf_counter: fix threaded task exit

Flushing counters in __exit_signal() with irqs disabled is not
a good idea as perf_counter_exit_task() acquires mutexes. So
flush it before acquiring the tasklist lock.

(Note, we still need a fix for when the PID has been unhashed.)

[ Impact: fix crash with inherited counters ]

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 6 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 16d74f13a3e7..73affd35e76d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -128,12 +128,6 @@ static void __exit_signal(struct task_struct *tsk)
                 sig = NULL; /* Marker for below. */
         }
 
-        /*
-         * Flush inherited counters to the parent - before the parent
-         * gets woken up by child-exit notifications.
-         */
-        perf_counter_exit_task(tsk);
-
         __unhash_process(tsk);
 
         /*
@@ -183,6 +177,13 @@ repeat:
         atomic_dec(&__task_cred(p)->user->processes);
 
         proc_flush_task(p);
+
+        /*
+         * Flush inherited counters to the parent - before the parent
+         * gets woken up by child-exit notifications.
+         */
+        perf_counter_exit_task(p);
+
         write_lock_irq(&tasklist_lock);
         tracehook_finish_release_task(p);
         __exit_signal(p);