On Fri, Aug 12, 2016 at 2:30 PM, Takashi Iwai <tiwai@xxxxxxx> wrote: > On Fri, 12 Aug 2016 14:15:16 +0200, >> >> >> > Also, the blocking read/write control isn't usually done by a >> >> > semaphore. Then you can handle the interrupt there. >> >> > >> >> > >> >> >> >> I actually wonder why, semaphores seemed perfect for this... Do you >> >> have some hints? >> > >> > Assume you want to interrupt the user-space app while it's being >> > blocked by the semaphore. With your code, you can't. >> > >> > >> >> You can - down_interruptible() is there for this exact reason. > > There is another blocking path: you keep semaphore down after > line6_hwdep_read() until line6_hwdep_push_message(). What happens if > user-space interrupts during that, and line6_hwdep_push_message() is > delayed or stall by some reason? > Actually, I think I don't see what's the "another path" here, could you please elaborate one more bit? I just want to make sure to not reimplement the same race using waitqueue... What's the point then? line6_hwdep_push_message() could get not scheduled for some while. So until it calls up(), line6_hwdep_read() will block on down_interruptible(), or until signal (in which case user gets -ERESTARTSYS). After up() is called, there are data in buffer... If line6_hwdep_read() returns after interrupt, no problem - the buffer will just continue to be filled and semaphore will be up()'d while there's free buffer space. Or until the device is closed... If I do the same via waitqueue, I will have the same problems, no? Maybe if you could post the steps where you see the race... At the same time, looking at __down_common(), it just does the standard waitqueue stuff (TASK_INTERRUPTIBLE + schedule()) (+counter in down())... So do you have some other race in mind? I'm running in circles, so surely you must :-) Sorry if I sound like a moron... and thanks for you time! -- Andrej _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
