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Commit f95d39d1 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

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



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: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a3f6dfb7

kernel/exit.c

+2 −2
Original line number Diff line number Diff line
@@ -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;