Re: [PATCH] Re: [BUG] Race condition with it_real_fn in kernel/itimer.c

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 2005-06-16 at 07:33 -0400, Steven Rostedt wrote:

> int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
> {
>         struct task_struct *tsk = current;
> 	static spinlock_t lock = SPIN_LOCK_UNLOCKED;
> 
> [...]
> 		spin_lock(&lock);
> 		spin_unlock(&tsk->sighand->siglock);
> 		del_timer_sync(&tsk->signal->real_timer);
> 		spin_lock(&tsk->sighand->siglock);
> 		spin_unlock(&lock);

OK, I just got out of bed, so I'm not too with it :-) 

This is pretty much a guaranteed deadlock!  So the first spin_lock needs
to go before the siglock. That should do it!


	case ITIMER_REAL:
		spin_lock_irq(&lock);
		spin_lock(&tsk->sighand->siglock);
		[...]
		spin_unlock(&tsk->sighand->siglock);
		del_timer_sync(&tsk->signal->real_timer);
		spin_lock(&tsk->sighand->siglock);
		spin_unlock(&lock);

We just need to keep two do_setitimer calls from grabbing the siglock.
That first string of code didn't prevent that.

-- Steve

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