On Wed, Oct 3, 2012 at 10:37 AM, Thomas Hellstrom <thellstrom@xxxxxxxxxx> wrote: >>> So if I understand you correctly, the reservation changes in TTM are >>> motivated by the >>> fact that otherwise, in the generic reservation code, lockdep can only be >>> annotated for a trylock and not a waiting lock, when it *is* in fact a >>> waiting lock. >>> >>> I'm completely unfamiliar with setting up lockdep annotations, but the >>> only >>> place a >>> deadlock might occur is if the trylock fails and we do a >>> wait_for_unreserve(). >>> Isn't it possible to annotate the call to wait_for_unreserve() just like >>> an >>> interruptible waiting lock >>> (that is always interrupted, but at least any deadlock will be catched?). >> >> Hm, I have to admit that idea hasn't crossed my mind, but it's indeed >> a hole in our current reservation lockdep annotations - since we're >> blocking for the unreserve, other threads could potential block >> waiting on us to release a lock we're holding already, resulting in a >> deadlock. >> >> Since no other locking primitive that I know of has this >> wait_for_unlocked interface, I don't know how we could map this in >> lockdep. One idea is to grab the lock and release it again immediately >> (only in the annotations, not the real lock ofc). But I need to check >> the lockdep code to see whether that doesn't trip it up. > > > I imagine doing the same as mutex_lock_interruptible() does in the > interrupted path should work... It simply calls the unlock lockdep annotation function if it breaks out. So doing a lock/unlock cycle in wait_unreserve should do what we want. And to properly annotate the ttm reserve paths we could just add an unconditional wait_unreserve call at the beginning like you suggested (maybe with #ifdef CONFIG_PROVE_LOCKING in case ppl freak out about the added atomic read in the uncontended case). -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
