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[PATCH] check_process_timers: fix possible lockup

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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>
This commit is contained in:
Oleg Nesterov 2006-06-15 20:11:15 +04:00 committed by Linus Torvalds
parent 88d113601c
commit 8f17fc20bf
1 changed files with 4 additions and 5 deletions
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9
kernel/posix-cpu-timers.c
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@ -1173,6 +1173,9 @@ static void check_process_timers(struct task_struct *tsk,
}
t = tsk;
do {
if (unlikely(t->flags & PF_EXITING))
continue;
ticks = cputime_add(cputime_add(t->utime, t->stime),
prof_left);
if (!cputime_eq(prof_expires, cputime_zero) &&
@ -1193,11 +1196,7 @@ static void check_process_timers(struct task_struct *tsk,
t->it_sched_expires > sched)) {
t->it_sched_expires = sched;
}
do {
t = next_thread(t);
} while (unlikely(t->flags & PF_EXITING));
} while (t != tsk);
} while ((t = next_thread(t)) != tsk);
}
}