[PATCH 1/2] ptrace: wait_task_zombie: do not account tracedsub-threads

[Oleg Nesterov]

The bug is ancient, the fix doesn't depend on other changes in -mm.

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@xxxxxxxxxx>

--- PTRACE/kernel/exit.c~1_WAIT_REPARENTED	2009-06-15 21:04:49.000000000 +0200
+++ PTRACE/kernel/exit.c	2009-06-15 22:26:02.000000000 +0200
@@ -1189,7 +1189,7 @@ static int wait_task_zombie(struct wait_
 
 	traced = ptrace_reparented(p);
 
-	if (likely(!traced)) {
+	if (likely(!traced) && likely(!task_detached(p))) {
 		struct signal_struct *psig;
 		struct signal_struct *sig;
 		struct task_cputime cputime;

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