As Peter pointed out, this barrier is not needed. utrace_set_events()
and tracehook_report_death() can rely on tasklist_lock.
utrace_set_events() checks ->exit_state == 0 and adds DEATH_EVENTS
under tasklist_lock. After exit_notify() sets ->exit_state under
write_lock(tasklist) we must see the change in flags.
utrace_set_events() does not set _UTRACE_DEATH_EVENTS if ->exit_state
was already set by exit_notify(), and after we set ->exit_state under
write_lock(tasklist) we must see the change in ->utrace_flags.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
include/linux/tracehook.h | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
--- UTRACE-PTRACE/include/linux/tracehook.h~1_REPORT_DEATH_KILL_MB
2009-11-18 21:16:23.000000000 +0100
+++ UTRACE-PTRACE/include/linux/tracehook.h 2009-12-12 16:32:39.000000000
+0100
@@ -626,17 +626,12 @@ static inline void tracehook_report_deat
int group_dead)
{
/*
- * This barrier ensures that our caller's setting of
- * @task->exit_state precedes checking @task->utrace_flags here.
* If utrace_set_events() was just called to enable
* UTRACE_EVENT(DEATH), then we are obliged to call
* utrace_report_death() and not miss it. utrace_set_events()
- * uses tasklist_lock to synchronize enabling the bit with the
- * actual change to @task->exit_state, but we need this barrier
- * to be sure we see a flags change made just before our caller
- * took the tasklist_lock.
+ * checks @task->exit_state under tasklist_lock to synchronize
+ * with exit_notify(), the caller.
*/
- smp_mb();
if (task_utrace_flags(task) & _UTRACE_DEATH_EVENTS)
utrace_report_death(task, death_cookie, group_dead, signal);
}
