Re: [I810_AUDIO] 1/x: Fix wait queue race in drain_dac

[Jeff Garzik <jgarzik@pobox.com>]

Herbert Xu wrote:
> On Sun, Jan 11, 2004 at 04:00:41PM -0500, Jeff Garzik wrote:
> 
>>Thanks much for these i810_audio patches.  I've been meaning to review 
>>them in-depth for some time.
> 
> 
> Thanks a lot for reviewing them.
> 
> 
>>Could you be kind and "spell out" the patch-1 race for me?
> 
> 
> Prior to the patch, if an interrupt occured between the count check
> and the setting of the current state the wait will timeout instead
> of waking up immediately.

hmmm, I'll have to think on this one a bit.  You are described observed 
behavior here... can you go a bit deeper, and describe what two code 
paths are racing?  I think I might a _different_ race in the code we're 
looking at, but I do not yet see the race you are describing :(


>>Also, it seems to me that you would want to check for signal_pending()
>>(a) just after the schedule_timeout(), and
>>(b) -after- testing the 'signals_allowed' variable  ;-)
> 
> 
> schedule() already checks for signals.

Well -- A signal won't be pending until after you call 
schedule_timeout() ;-)  A signal, particularly SIGINT, might even occur 
_during_ the schedule_timeout().

	Jeff