On 04/04, Srivatsa Vaddagiri wrote:
>
> On Wed, Apr 04, 2007 at 07:28:28PM +0400, Oleg Nesterov wrote:
> >
> > worker_thread:
> >
> > for (;;) {
> > try_to_freeze();
> >
> > prepare_to_wait();
> > if (...)
> > schedule();
> > finish_wait();
> > }
> >
> > This is racy, we can miss freeze_process()->signal_wake_up() if it happens
> > between try_to_freeze() and prepare_to_wait(). We have to check TIF_FREEZE
> > before entering schedule() if we want to fix this race.
>
> Yes that needs a fix as well. Oh dear, freezer is so fragile to break!
>
> > Should we? I don't know. This will uglify the code, and the probability
> > of this race is very low.
>
> Would be nice to fix IMO. Atleast serves to show "how to make your code
> freezer friendly".
This is funny. I "noticed" this race a long ago, when the ->freezeable flag
was introduced. However, looking at 2.6.20 I see that the patch was correct,
and this race was in fact introduced by me in
[PATCH 1/1] workqueue: don't migrate pending works from the dead CPU
http://marc.info/?l=linux-kernel&m=117062192709871
I'll send a fix on weekend.
Oleg.
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