On Thu, 25 Oct 2007, Maxim Levitsky wrote:
> Hi,
>
> Recently, trying to fix saa7134 suspend/resume problems I found that there
> is a race between IRQ handler and .suspend , and that I cant let driver access the device
> while its in D3 since it can lock up some systems.
>
> Now I am looking to fix those issues in two drivers that have my .suspend/.resume routines.
> the saa7134 capture chip and dmfe, the davicom network driver.
>
> Looking through the dmfe code, I noticed yet another possible race.
> A race between the .suspend, and a timer that serves both as a watchdog, and link state detector.
> Again I need to prevent it from running during the suspend/resume, but how?
>
> I can use del_timer in .suspend, and mod_timer in .resume, but that doesn't protect against
> race with already running timer.
> I can use del_timer_sync, but it states that it is useless if timer re-enables itself, and I agree with that.
> In dmfe case the timer does re-enable itself.
That comment isn't right. del_timer_sync works perfectly well even if
the timer routine re-enables itself, provided it stops doing so after a
small number of iterations.
> I can put checks in the timer for ->insuspend, and don't re enable it if set,
> but that opens a new can of worms with memory barriers, etc...
You don't have to worry about any of that stuff. Just check the
insuspend flag and don't re-enable the timer if it is set. Even
without any memory barriers, the timer routine won't iterate more than
once or twice.
Alan Stern
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