On Wed, 2024-09-11 at 15:42 -0400, 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 > way for future uses by both filesystems and lock managers alike. > > Criticism welcomed, > Ben > > Benjamin Coddington (4): > fs: Introduce FOP_ASYNC_LOCK > gfs2/ocfs2: set FOP_ASYNC_LOCK > NLM/NFSD: Fix lock notifications for async-capable filesystems > exportfs: Remove EXPORT_OP_ASYNC_LOCK > > Documentation/filesystems/nfs/exporting.rst | 7 ------- > fs/gfs2/export.c | 1 - > fs/gfs2/file.c | 2 ++ > fs/lockd/svclock.c | 5 ++--- > fs/nfsd/nfs4state.c | 19 ++++--------------- > fs/ocfs2/export.c | 1 - > fs/ocfs2/file.c | 2 ++ > include/linux/exportfs.h | 13 ------------- > include/linux/filelock.h | 5 +++++ > include/linux/fs.h | 2 ++ > 10 files changed, 17 insertions(+), 40 deletions(-) > Thanks for fixing this up, Ben! Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
