NFS: Ensure we always hold the BKL when dereferencing inode->i_flock

Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/delegation.c

@@ -70,15 +70,24 @@ static int nfs_delegation_claim_locks(struct nfs_open_context *ctx, struct nfs4_
 	struct file_lock *fl;
 	int status = 0;
 
+	if (inode->i_flock == NULL)
+		goto out;
+
+	/* Protect inode->i_flock using the BKL */
+	lock_kernel();
 	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
 		if (!(fl->fl_flags & (FL_POSIX|FL_FLOCK)))
 			continue;
 		if (nfs_file_open_context(fl->fl_file) != ctx)
 			continue;
+		unlock_kernel();
 		status = nfs4_lock_delegation_recall(state, fl);
 		if (status < 0)
-			break;
+			goto out;
+		lock_kernel();
 	}
+	unlock_kernel();
+out:
 	return status;
 }
 
@@ -256,7 +265,10 @@ static int __nfs_inode_return_delegation(struct inode *inode, struct nfs_delegat
 	struct nfs_inode *nfsi = NFS_I(inode);
 
 	nfs_msync_inode(inode);
-	/* Guard against new delegated open calls */
+	/*
+	 * Guard against new delegated open/lock/unlock calls and against
+	 * state recovery
+	 */
 	down_write(&nfsi->rwsem);
 	nfs_delegation_claim_opens(inode, &delegation->stateid);
 	up_write(&nfsi->rwsem);

fs/nfs/nfs4state.c

@@ -847,12 +847,19 @@ static int nfs4_reclaim_locks(struct nfs4_state *state, const struct nfs4_state_
 	struct file_lock *fl;
 	int status = 0;
 
+	if (inode->i_flock == NULL)
+		return 0;
+
+	/* Guard against delegation returns and new lock/unlock calls */
 	down_write(&nfsi->rwsem);
+	/* Protect inode->i_flock using the BKL */
+	lock_kernel();
 	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
 		if (!(fl->fl_flags & (FL_POSIX|FL_FLOCK)))
 			continue;
 		if (nfs_file_open_context(fl->fl_file)->state != state)
 			continue;
+		unlock_kernel();
 		status = ops->recover_lock(state, fl);
 		switch (status) {
 			case 0:
@@ -875,7 +882,9 @@ static int nfs4_reclaim_locks(struct nfs4_state *state, const struct nfs4_state_
 				/* kill_proc(fl->fl_pid, SIGLOST, 1); */
 				status = 0;
 		}
+		lock_kernel();
 	}
+	unlock_kernel();
 out:
 	up_write(&nfsi->rwsem);
 	return status;