Re: [libvirt] [PATCH v5 1/3] nwfilter: Convert _virNWFilterObj to use virObjectRWLockable

>> } >> >> >> +static void >> +virNWFilterObjPromoteToWrite(virNWFilterObjPtr obj) >> +{ >> + virObjectRWUnlock(obj); >> + virObjectRWLockWrite(obj); >> +} > > How can this not deadlock? This will work only if @obj is locked exactly > once. But since we allow recursive locks any lock() that happens in the > 2nd level must deadlock with this. On the other hand, there's no such > case in the code currently. But that doesn't stop anybody from calling > PromoteWrite() without understanding its limitations. > > Maybe the fact that we need recursive lock for NWFilterObj means it's > not a good candidate for virObjectRWLocable? It is still a good > candidate for virObject though. > > Or if you want to spend extra time on this, maybe introducing > virObjectRecursiveLockable may be worth it (terrible name, I know). I can't remember exactly call trace scenarios that meant we required recursive locking. I vaguely recall is was related to fact that we have an alternative entry point into the nwfilter code that's triggered by the virt drivers. I'm thus vaguely hoping that when we split nwfilter off into a separate daemon from virt driver, the need for recursive lockingn would magically disappear. I could be completely wrong though :-)