nfs: don't allow reexport reclaims

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@redhat.com>
Acked-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

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 -ENOGRACE;
+
 	/* No mandatory locks over NFS */
 	if (__mandatory_lock(inode) && fl->fl_type != F_UNLCK)
 		goto out_err;

fs/nfsd/nfs4state.c

@@ -6903,6 +6903,9 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	if (!locks_in_grace(net) && lock->lk_reclaim)
 		goto out;
 
+	if (lock->lk_reclaim)
+		fl_flags |= FL_RECLAIM;
+
 	fp = lock_stp->st_stid.sc_file;
 	switch (lock->lk_type) {
 		case NFS4_READW_LT:

fs/nfsd/nfsproc.c

@@ -881,6 +881,7 @@ nfserrno (int errno)
 		{ nfserr_serverfault, -ENFILE },
 		{ nfserr_io, -EUCLEAN },
 		{ nfserr_perm, -ENOKEY },
+		{ nfserr_no_grace, -ENOGRACE},
 	};
 	int	i;
 

include/linux/errno.h

@@ -31,5 +31,6 @@
 #define EJUKEBOX	528	/* Request initiated, but will not complete before timeout */
 #define EIOCBQUEUED	529	/* iocb queued, will get completion event */
 #define ERECALLCONFLICT	530	/* conflict with recalled state */
+#define ENOGRACE	531	/* NFS file lock reclaim refused */
 
 #endif

include/linux/fs.h

@@ -997,6 +997,7 @@ static inline struct file *get_file(struct file *f)
 #define FL_UNLOCK_PENDING	512 /* Lease is being broken */
 #define FL_OFDLCK	1024	/* lock is "owned" by struct file */
 #define FL_LAYOUT	2048	/* outstanding pNFS layout */
+#define FL_RECLAIM	4096	/* reclaiming from a reboot server */
 
 #define FL_CLOSE_POSIX (FL_POSIX | FL_CLOSE)