NFSv4: Ensure delegation recall and byte range lock removal don't conflict

Add a mutex to the struct nfs4_state_owner to ensure that delegation
recall doesn't conflict with byte range lock removal.

Note that we nest the new mutex _outside_ the state manager reclaim
protection (nfsi->rwsem) in order to avoid deadlocks.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/delegation.c

@@ -71,8 +71,10 @@ static int nfs_delegation_claim_locks(struct nfs_open_context *ctx, struct nfs4_
 	int status = 0;
 
 	if (inode->i_flock == NULL)
-		goto out;
+		return 0;
 
+	if (inode->i_flock == NULL)
+		goto out;
 	/* Protect inode->i_flock using the file locks lock */
 	lock_flocks();
 	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
@@ -113,12 +115,15 @@ static int nfs_delegation_claim_opens(struct inode *inode, const nfs4_stateid *s
 		get_nfs_open_context(ctx);
 		spin_unlock(&inode->i_lock);
 		sp = state->owner;
+		/* Block nfs4_proc_unlck */
+		mutex_lock(&sp->so_delegreturn_mutex);
 		seq = raw_seqcount_begin(&sp->so_reclaim_seqcount);
 		err = nfs4_open_delegation_recall(ctx, state, stateid);
 		if (!err)
 			err = nfs_delegation_claim_locks(ctx, state);
 		if (!err && read_seqcount_retry(&sp->so_reclaim_seqcount, seq))
 			err = -EAGAIN;
+		mutex_unlock(&sp->so_delegreturn_mutex);
 		put_nfs_open_context(ctx);
 		if (err != 0)
 			return err;

fs/nfs/nfs4_fs.h

@@ -93,6 +93,7 @@ struct nfs4_state_owner {
 	struct list_head     so_states;
 	struct nfs_seqid_counter so_seqid;
 	seqcount_t	     so_reclaim_seqcount;
+	struct mutex	     so_delegreturn_mutex;
 };
 
 enum {

fs/nfs/nfs4proc.c

@@ -4485,7 +4485,9 @@ static struct rpc_task *nfs4_do_unlck(struct file_lock *fl,
 
 static int nfs4_proc_unlck(struct nfs4_state *state, int cmd, struct file_lock *request)
 {
-	struct nfs_inode *nfsi = NFS_I(state->inode);
+	struct inode *inode = state->inode;
+	struct nfs4_state_owner *sp = state->owner;
+	struct nfs_inode *nfsi = NFS_I(inode);
 	struct nfs_seqid *seqid;
 	struct nfs4_lock_state *lsp;
 	struct rpc_task *task;
@@ -4495,12 +4497,17 @@ static int nfs4_proc_unlck(struct nfs4_state *state, int cmd, struct file_lock *
 	status = nfs4_set_lock_state(state, request);
 	/* Unlock _before_ we do the RPC call */
 	request->fl_flags |= FL_EXISTS;
+	/* Exclude nfs_delegation_claim_locks() */
+	mutex_lock(&sp->so_delegreturn_mutex);
+	/* Exclude nfs4_reclaim_open_stateid() - note nesting! */
 	down_read(&nfsi->rwsem);
 	if (do_vfs_lock(request->fl_file, request) == -ENOENT) {
 		up_read(&nfsi->rwsem);
+		mutex_unlock(&sp->so_delegreturn_mutex);
 		goto out;
 	}
 	up_read(&nfsi->rwsem);
+	mutex_unlock(&sp->so_delegreturn_mutex);
 	if (status != 0)
 		goto out;
 	/* Is this a delegated lock? */

fs/nfs/nfs4state.c

@@ -519,6 +519,7 @@ nfs4_alloc_state_owner(struct nfs_server *server,
 	atomic_set(&sp->so_count, 1);
 	INIT_LIST_HEAD(&sp->so_lru);
 	seqcount_init(&sp->so_reclaim_seqcount);
+	mutex_init(&sp->so_delegreturn_mutex);
 	return sp;
 }