Op 27-05-13 13:15, Peter Zijlstra schreef: > On Mon, May 27, 2013 at 12:52:00PM +0200, Maarten Lankhorst wrote: >> The reason ttm needed it was because there was another lock that interacted >> with the ctx lock in a weird way. The ww lock it was using was inverted with another >> lock, so it had to grab that lock first, perform a trylock on the ww lock, and if that failed >> unlock the lock, wait for it to be unlocked, then retry the same thing again. >> I'm so glad I managed to fix that mess, if you really need ww_mutex_trylock with a ctx, >> it's an indication your locking is wrong. >> >> For ww_mutex_trylock with a context to be of any use you would also need to return >> 0 or a -errno, (-EDEADLK, -EBUSY (already locked by someone else), or -EALREADY). >> This would make the trylock very different from other trylocks, and very confusing because >> if (ww_mutex_trylock(lock, ctx)) would not do what you would think it would do. > Yuck ;-) > > Anyway, what I was thinking of is something like: > > T0 T1 > > try A > lock B > lock B > lock A > > Now, if for some reason T1 won the lottery such that T0 would have to be > wounded, T0's context would indicate its the first entry and not return > -EDEADLK. And this sounds like something lockdep is designed to complain about. Nothing stops you from doing try A then doing try B, which would be the correct way to deal with this situation. Why would you trylock one, and then not do the same for another? > OTOH, anybody doing creative things like that might well deserve > whatever they get ;-) Indeed! >>> The thing is; if there could exist something like: >>> >>> ww_mutex_trylock(struct ww_mutex *, struct ww_acquire_ctx *ctx); >>> >>> Then we should not now take away that name and make it mean something >>> else; namely: ww_mutex_trylock_single(). >>> >>> Unless we want to allow .ctx=NULL to mean _single. >>> >>> As to why I proposed that (.ctx=NULL meaning _single); I suppose because >>> I'm a minimalist at heart. >> Minimalism isn't bad, it's just knowing when to sto > :-) > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
