Re: PATCH: Race in 2.6.0-test2 timer code

From: Ingo Molnar (mingo@elte.hu)
Date: Wed Jul 30 2003 - 05:31:23 EST


On Wed, 30 Jul 2003, Andrea Arcangeli wrote:

>
> cpu0 cpu1
> ------------ --------------------
>
> do_setitimer
> it_real_fn
> del_timer_sync add_timer -> crash

would you mind to elaborate the precise race? I cannot see how the above
sequence could crash on current 2.6:

del_timer_sync() takes the base pointer in timer->base and locks it, then
checks whether the timer has this base or not and repeats the sequence if
not. add_timer() locks the current CPU's base, then installs the timer and
sets timer->base. Where's the race?

        Ingo

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