On Wed, Sep 11, 2024 at 03:42:56PM GMT, Benjamin Coddington wrote: > Last year both GFS2 and OCFS2 had some work done to make their locking more > robust when exported over NFS. Unfortunately, part of that work caused both > NLM (for NFS v3 exports) and kNFSD (for NFSv4.1+ exports) to no longer send > lock notifications to clients. > > This in itself is not a huge problem because most NFS clients will still > poll the server in order to acquire a conflicted lock, but now that I've > noticed it I can't help but try to fix it because there are big advantages > for setups that might depend on timely lock notifications, and we've > supported that as a feature for a long time. > > Its important for NLM and kNFSD that they do not block their kernel threads > inside filesystem's file_lock implementations because that can produce > deadlocks. We used to make sure of this by only trusting that > posix_lock_file() can correctly handle blocking lock calls asynchronously, > so the lock managers would only setup their file_lock requests for async > callbacks if the filesystem did not define its own lock() file operation. > > However, when GFS2 and OCFS2 grew the capability to correctly > handle blocking lock requests asynchronously, they started signalling this > behavior with EXPORT_OP_ASYNC_LOCK, and the check for also trusting > posix_lock_file() was inadvertently dropped, so now most filesystems no > longer produce lock notifications when exported over NFS. > > I tried to fix this by simply including the old check for lock(), but the > resulting include mess and layering violations was more than I could accept. > There's a much cleaner way presented here using an fop_flag, which while > potentially flag-greedy, greatly simplifies the problem and grooms the It's fine. I've explicitly added the fop_flags so that stuff like this we would not want to put into f->f_mode can live there. > way for future uses by both filesystems and lock managers alike.
