On Mon, 2021-06-14 at 16:03 -0400, bfields@xxxxxxxxxxxx wrote: > On Mon, Jun 14, 2021 at 07:53:52PM +0000, Trond Myklebust wrote: > > On Mon, 2021-06-14 at 15:34 -0400, J. Bruce Fields wrote: > > > On Mon, Jun 14, 2021 at 02:56:55PM +0000, Trond Myklebust wrote: > > > > On Mon, 2021-06-14 at 10:48 -0400, J. Bruce Fields wrote: > > > > > From: "J. Bruce Fields" <bfields@xxxxxxxxxx> > > > > > > > > > > In the reexport case, nfsd is currently passing along locks > > > > > with > > > > > the > > > > > reclaim bit set. The client sends a new lock request, which > > > > > is > > > > > granted > > > > > if there's currently no conflict--even if it's possible a > > > > > conflicting > > > > > lock could have been briefly held in the interim. > > > > > > > > > > We don't currently have any way to safely grant reclaim, so > > > > > for > > > > > now > > > > > let's just deny them all. > > > > > > > > > > I'm doing this by passing the reclaim bit to nfs and letting > > > > > it > > > > > fail > > > > > the > > > > > call, with the idea that eventually the client might be able > > > > > to > > > > > do > > > > > something more forgiving here. > > > > > > > > > > Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx> > > > > > --- > > > > > fs/nfs/file.c | 3 +++ > > > > > fs/nfsd/nfs4state.c | 3 +++ > > > > > fs/nfsd/nfsproc.c | 1 + > > > > > include/linux/fs.h | 1 + > > > > > 4 files changed, 8 insertions(+) > > > > > > > > > > diff --git a/fs/nfs/file.c b/fs/nfs/file.c > > > > > index 1fef107961bc..35a29b440e3e 100644 > > > > > --- a/fs/nfs/file.c > > > > > +++ b/fs/nfs/file.c > > > > > @@ -806,6 +806,9 @@ int nfs_lock(struct file *filp, int cmd, > > > > > struct > > > > > file_lock *fl) > > > > > > > > > > nfs_inc_stats(inode, NFSIOS_VFSLOCK); > > > > > > > > > > + if (fl->fl_flags & FL_RECLAIM) > > > > > + return -NFSERR_NO_GRACE; > > > > > > > > NACK. nfs_lock() is required to return a POSIX error. I know > > > > that > > > > right > > > > now, nfsd is the only thing setting FL_RECLAIM, but we can't > > > > guarantee > > > > that will always be the case. > > > > > > Setting FL_RECLAIM tells the filesystem that you're prepared to > > > handle > > > NFSERR_NO_GRACE. I'm not seeing the risk. > > > > You are using a function that is exposed to the VFS. On error, that > > function is expected to return a value that is a Linux error > > between -1 > > and -4095. > > Or 1, actually (FILE_LOCK_DEFERRED). > > > I suggest adding an error value ENOGRACE to include/linux/errno.h. > > I can live with that, but I'm still curious what exactly you're > worried > about. > I want to avoid the kind of issues we've be met with earlier when mixing types just because they happened to be integer valued. We introduced the mixing of POSIX/Linux and NFS errors in the NFS client back in the 1990s, and that was a mistake that we're still paying for. For instance, the value ERR_PTR(-NFSERR_NO_GRACE) will be happily declared as a valid pointer by the IS_ERR() test, and every so often we find an Oops around that issue because someone used the return value from a function that they thought was POSIX/Linux error valued, because it usually is returning POSIX errors. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
