NFS: avoid spurious warning of lost lock that is being unlocked.

When the NFSv4 state manager recovers state after a server restart, it
reports that locks have been lost if it finds any lock state for which
recovery hasn't been successful.  i.e. any for which
NFS_LOCK_INITIALIZED is not set.

However it only tries to recover locks that are still linked to
inode->i_flctx.  So if a lock has been removed from inode->i_flctx, but
the state for that lock has not yet been destroyed, then a spurious
warning results.

nfs4_proc_unlck() calls locks_lock_inode_wait() - which removes the lock
from ->i_flctx - before sending the unlock request to the server and
before the final nfs4_put_lock_state() is called.  This allows a window
in which a spurious warning can be produced.

So add a new flag NFS_LOCK_UNLOCKING which is set once the decision has
been made to unlock the lock.  This will prevent it from triggering any
warning.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4_fs.h

@@ -149,6 +149,7 @@ struct nfs4_lock_state {
 	struct nfs4_state *	ls_state;	/* Pointer to open state */
 #define NFS_LOCK_INITIALIZED 0
 #define NFS_LOCK_LOST        1
+#define NFS_LOCK_UNLOCKING   2
 	unsigned long		ls_flags;
 	struct nfs_seqid_counter	ls_seqid;
 	nfs4_stateid		ls_stateid;

fs/nfs/nfs4proc.c

@@ -7023,12 +7023,13 @@ static int nfs4_proc_unlck(struct nfs4_state *state, int cmd, struct file_lock *
 		mutex_unlock(&sp->so_delegreturn_mutex);
 		goto out;
 	}
+	lsp = request->fl_u.nfs4_fl.owner;
+	set_bit(NFS_LOCK_UNLOCKING, &lsp->ls_flags);
 	up_read(&nfsi->rwsem);
 	mutex_unlock(&sp->so_delegreturn_mutex);
 	if (status != 0)
 		goto out;
 	/* Is this a delegated lock? */
-	lsp = request->fl_u.nfs4_fl.owner;
 	if (test_bit(NFS_LOCK_INITIALIZED, &lsp->ls_flags) == 0)
 		goto out;
 	alloc_seqid = NFS_SERVER(inode)->nfs_client->cl_mvops->alloc_seqid;

fs/nfs/nfs4state.c

@@ -1619,7 +1619,8 @@ static int __nfs4_reclaim_open_state(struct nfs4_state_owner *sp, struct nfs4_st
 		spin_lock(&state->state_lock);
 		list_for_each_entry(lock, &state->lock_states, ls_locks) {
 			trace_nfs4_state_lock_reclaim(state, lock);
-			if (!test_bit(NFS_LOCK_INITIALIZED, &lock->ls_flags))
+			if (!test_bit(NFS_LOCK_INITIALIZED, &lock->ls_flags) &&
+			    !test_bit(NFS_LOCK_UNLOCKING, &lock->ls_flags))
 				*lost_locks += 1;
 		}
 		spin_unlock(&state->state_lock);