Commit f95d39d1 authored Jun 17, 2009 by Oleg Nesterov Committed by Linus Torvalds Jun 18, 2009

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: 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>

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;

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