[PATCH] check_process_timers: fix possible lockup
commit8f17fc20bfb75bcec4cfeda789738979c8338fdc
authorOleg Nesterov <oleg@tv-sign.ru>
Thu, 15 Jun 2006 16:11:15 +0000 (15 20:11 +0400)
committerLinus Torvalds <torvalds@g5.osdl.org>
Sat, 17 Jun 2006 17:52:13 +0000 (17 10:52 -0700)
treeec84c5222de58b4d26507c892d0b8f828a6dce7e
parent88d113601ca19c82feb038438c8c5db502d146f9
[PATCH] check_process_timers: fix possible lockup

If the local timer interrupt happens just after do_exit() sets PF_EXITING
(and before it clears ->it_xxx_expires) run_posix_cpu_timers() will call
check_process_timers() with tasklist_lock + ->siglock held and

check_process_timers:

t = tsk;
do {
....

do {
t = next_thread(t);
} while (unlikely(t->flags & PF_EXITING));
} while (t != tsk);

the outer loop will never stop.

Actually, the window is bigger.  Another process can attach the timer
after ->it_xxx_expires was cleared (see the next commit) and the 'if
(PF_EXITING)' check in arm_timer() is racy (see the one after that).

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
kernel/posix-cpu-timers.c