ptrace: wait_task_zombie: do not account traced sub-threads
Oleg Nesterov [Thu, 18 Jun 2009 23:49:11 +0000 (16:49 -0700)]
The bug is ancient.

If we trace the sub-thread of our natural child and this sub-thread exits,
we update parent->signal->cxxx fields.  But we should not do this until
the whole thread-group exits, otherwise we account this thread (and all
other live threads) twice.

Add the task_detached() check.  No need to check thread_group_empty(),
wait_consider_task()->delay_group_leader() already did this.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Vitaly Mayatskikh <vmayatsk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

index 13ae640..628d41f 100644 (file)
@@ -1197,8 +1197,11 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
        }
 
        traced = ptrace_reparented(p);
-
-       if (likely(!traced)) {
+       /*
+        * It can be ptraced but not reparented, check
+        * !task_detached() to filter out sub-threads.
+        */
+       if (likely(!traced) && likely(!task_detached(p))) {
                struct signal_struct *psig;
                struct signal_struct *sig;