On 16.12.2021 20:20, J. Bruce Fields wrote: > From: "J. Bruce Fields" <bfields@xxxxxxxxxx> > > NFSv4.1 supports an optional lock notification feature which notifies > the client when a lock comes available. (Normally NFSv4 clients just > poll for locks if necessary.) To make that work, we need to request a > blocking lock from the filesystem. > > We turned that off for NFS in f657f8eef3ff "nfs: don't atempt blocking > locks on nfs reexports" because it actually blocks the nfsd thread while > waiting for the lock. > > Thanks to Vasily Averin for pointing out that NFS isn't the only > filesystem with that problem. > > Any filesystem that leaves ->lock NULL will use posix_lock_file(), which > does the right thing. Simplest is just to assume that any filesystem > that defines its own ->lock is not safe to request a blocking lock from. > > So, this patch mostly reverts f657f8eef3ff and b840be2f00c0, and instead > uses a check of ->lock (Vasily's suggestion) to decide whether to > support blocking lock notifications on a given filesystem. Also add a > little documentation. > > Perhaps someday we could add back an export flag later to allow > filesystems with "good" ->lock methods to support blocking lock > notifications. > > Reported-by: Vasily Averin <vvs@xxxxxxxxxxxxx> > Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx> Reviewed-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
