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do_wait: fix the theoretical race with stop/trace/cont

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do_wait:

	current->state = TASK_INTERRUPTIBLE;

	read_lock(&tasklist_lock);
	... search for the task to reap ...

In theory, the ->state changing can leak into the critical section.  Since
the child can change its status under read_lock(tasklist) in parallel
(finish_stop/ptrace_stop), we can miss the wakeup if __wake_up_parent()
sees us in TASK_RUNNING state.  Add the barrier.

Also, use __set_current_state() to set TASK_RUNNING.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2009-06-17 16:27:42 -07:00 committed by Linus Torvalds
parent a3f6dfb729
commit f95d39d10f
1 changed files with 2 additions and 2 deletions
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4
kernel/exit.c
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@ -1581,7 +1581,7 @@ repeat:
(!wo->wo_pid || hlist_empty(&wo->wo_pid->tasks[wo->wo_type])))
goto notask;
current->state = TASK_INTERRUPTIBLE;
set_current_state(TASK_INTERRUPTIBLE);
read_lock(&tasklist_lock);
tsk = current;
do {
@ -1608,7 +1608,7 @@ notask:
}
}
end:
current->state = TASK_RUNNING;
__set_current_state(TASK_RUNNING);
remove_wait_queue(&current->signal->wait_chldexit,&wait);
if (wo->wo_info) {
struct siginfo __user *infop = wo->wo_info;