releases/2.6.38.4/perf-fix-task-context-scheduling.patch

   1 From ab711fe08297de1485fff0a366e6db8828cafd6a Mon Sep 17 00:00:00 2001
   2 From: Peter Zijlstra <a.p.zijlstra@chello.nl>
   3 Date: Thu, 31 Mar 2011 10:29:26 +0200
   4 Subject: perf: Fix task context scheduling
   5
   6 From: Peter Zijlstra <a.p.zijlstra@chello.nl>
   7
   8 commit ab711fe08297de1485fff0a366e6db8828cafd6a upstream.
   9
  10 Jiri reported:
  11
  12  |
  13  | - once an event is created by sys_perf_event_open, task context
  14  |   is created and it stays even if the event is closed, until the
  15  |   task is finished ... thats what I see in code and I assume it's
  16  |   correct
  17  |
  18  | - when the task opens event, perf_sched_events jump label is
  19  |   incremented and following callbacks are started from scheduler
  20  |
  21  |         __perf_event_task_sched_in
  22  |         __perf_event_task_sched_out
  23  |
  24  |   These callback *in/out set/unset cpuctx->task_ctx value to the
  25  |   task context.
  26  |
  27  | - close is called on event on CPU 0:
  28  |         - the task is scheduled on CPU 0
  29  |         - __perf_event_task_sched_in is called
  30  |         - cpuctx->task_ctx is set
  31  |         - perf_sched_events jump label is decremented and == 0
  32  |         - __perf_event_task_sched_out is not called
  33  |         - cpuctx->task_ctx on CPU 0 stays set
  34  |
  35  | - exit is called on CPU 1:
  36  |         - the task is scheduled on CPU 1
  37  |         - perf_event_exit_task is called
  38  |         - task_ctx_sched_out unsets cpuctx->task_ctx on CPU 1
  39  |         - put_ctx destroys the context
  40  |
  41  | - another call of perf_rotate_context on CPU 0 will use invalid
  42  |   task_ctx pointer, and eventualy panic.
  43  |
  44
  45 Cure this the simplest possibly way by partially reverting the
  46 jump_label optimization for the sched_out case.
  47
  48 Reported-and-tested-by: Jiri Olsa <jolsa@redhat.com>
  49 Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
  50 Cc: Oleg Nesterov <oleg@redhat.com>
  51 LKML-Reference: <1301520405.4859.213.camel@twins>
  52 Signed-off-by: Ingo Molnar <mingo@elte.hu>
  53 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
  54
  55 ---
  56  include/linux/perf_event.h |    2 +-
  57  1 file changed, 1 insertion(+), 1 deletion(-)
  58
  59 --- a/include/linux/perf_event.h
  60 +++ b/include/linux/perf_event.h
  61 @@ -1052,7 +1052,7 @@ void perf_event_task_sched_out(struct ta
  62  {
  63         perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);
  64
  65 -       COND_STMT(&perf_task_events, __perf_event_task_sched_out(task, next));
  66 +       __perf_event_task_sched_out(task, next);
  67  }
  68
  69  extern void perf_event_mmap(struct vm_area_struct *vma);