Re: swallowed wakeup in hiddev

Am Mittwoch, 31. Januar 2007 14:18 schrieb Jiri Kosina:
> > > with both the flags unset (if a timeout doesn't happen sooner, which is 
> > > OK). If this "final" wake_up() is called before the usbhid_wait_io() is 
> > > called, this is also OK, because then the condition will evaluate to true 
> > > and the task won't event sleep on the waitqueue.
> > Who tells you that the flags will still be cleared? Somebody else may
> > have called usbhid_submit_report() by the time you check the flags.
> 
> Yes, but in such case it is again guaranteed that there will be wake_up() 
> coming from the URB submission which happened later - either the flags are 
> cleared, or wake_up() will eventually happen (you are right that it might 
> possibly be wake_up() corresponding to submission of URB submitted later, 
> but does that matter?).

Yes, as you cannot make sure it'll come before the timeout strikes, nor
can you make sure the condition will be true when a second URB finishes.
This logic can fail under load.

	Regards
		Oliver

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