Re: PATCH: Race in 2.6.0-test2 timer code

[Andrea Arcangeli <andrea@suse.de>]

On Wed, Jul 30, 2003 at 09:34:40AM +0200, Ingo Molnar wrote:
> 
> On Wed, 30 Jul 2003, Andrea Arcangeli wrote:
> 
> > The thing triggered simply by running setitimer in one function, while
> > the it_real_fn was running in the other cpu. I don't see how 2.6 can
> > have fixed this, it_real_fun can still trivially call add_timer while
> > you run inside do_setitimer in 2.6 too. [...]
> 
> This is not a race that can happen. itimer does this:
> 
> 	del_timer_sync();
> 	add_timer();
> 
> how can the add_timer() still happen while it_real_fn is still running on 
> another CPU?

it's not add_timer against add_timer in this case, it's del_timer_sync
against add_timer.


	cpu0			cpu1
	------------		--------------------

	do_setitimer
				it_real_fn
	del_timer_sync		add_timer	-> crash

Andrea