do_wait: fix the theoretical race with stop/trace/cont
commitf95d39d10fe7d47336e65172f52bf64e0096f983
authorOleg Nesterov <oleg@redhat.com>
Wed, 17 Jun 2009 23:27:42 +0000 (17 16:27 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 18 Jun 2009 20:03:53 +0000 (18 13:03 -0700)
tree14b469b68455968dfd707695083ece72287dfaab
parenta3f6dfb7295facb0505b5beca5a7ce48b0612379
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>
kernel/exit.c