Messages in this thread Patch in this message | | | Subject | Re: [PATCH] fix send_sigqueue() vs thread exit race | From | Thomas Gleixner <> | Date | Sun, 21 Aug 2005 23:24:28 +0200 |
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Oleg,
On Sun, 2005-08-21 at 14:59 +0400, Oleg Nesterov wrote: > CPU_0 CPU_1 > > release_task: posix_timer_fn: > write_lock(tasklist); lock(timer->it_lock); > > exit_timers: send_sigxxx(); > lock(timer->it_lock) read_lock(tasklist); > > Deadlock. > > Dear cc-list, what do you think?
The patch below on top of your patch should solve this. We don't need tasklist_lock to check p->flags. As you pointed out p cannot be invalid in send_sigqueue as it's protected by get_task_struct() in create_timer()
For send_group_sigqueue it's protected by exit_itimers() waiting for k_itimer.it_lock.
It still does not solve the ugly dependency on tasklist_lock but at least the race and the deadlock are fixed.
tglx
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
--- linux-2.6.13-rc6.signal/kernel/signal.oleg.c 2005-08-21 23:07:03.000000000 +0200 +++ linux-2.6.13-rc6.signal/kernel/signal.c 2005-08-21 23:09:07.000000000 +0200 @@ -1381,11 +1381,14 @@ send_sigqueue(int sig, struct sigqueue * int ret = 0; BUG_ON(!(q->flags & SIGQUEUE_PREALLOC)); - read_lock(&tasklist_lock); - if (unlikely(p->flags & PF_EXITING)) { - ret = -1; - goto out_err; +retry: + if (unlikely(p->flags & PF_EXITING)) + return -1; + + if ((unlikely(!read_trylock(&tasklist_lock))) { + cpu_relax(); + goto retry; } spin_lock_irqsave(&p->sighand->siglock, flags); @@ -1414,7 +1417,6 @@ send_sigqueue(int sig, struct sigqueue * out: spin_unlock_irqrestore(&p->sighand->siglock, flags); -out_err: read_unlock(&tasklist_lock); return ret; @@ -1427,7 +1429,14 @@ send_group_sigqueue(int sig, struct sigq int ret = 0; BUG_ON(!(q->flags & SIGQUEUE_PREALLOC)); - read_lock(&tasklist_lock); +retry: + if (unlikely(p->flags & PF_EXITING)) + return -1; + + if (unlikely(!read_trylock(&tasklist_lock))) { + cpu_relax(); + goto retry; + } spin_lock_irqsave(&p->sighand->siglock, flags); handle_stop_signal(sig, p); --- linux-2.6.13-rc6.signal/kernel/posix-timers.oleg.c 2005-08-21 23:09:58.000000000 +0200 +++ linux-2.6.13-rc6.signal/kernel/posix-timers.c 2005-08-21 23:19:42.000000000 +0200 @@ -501,7 +501,8 @@ static void posix_timer_fn(unsigned long remove_from_abslist(timr); } - if (posix_timer_event(timr, si_private)) + /* Do not rearm the timer, when we are exiting */ + if (posix_timer_event(timr, si_private) > 0) /* * signal was not sent because of sig_ignor * we will not get a call back to restart it AND
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