NFSv4: nfs_atomic_open() can race when looking up a non-regular file

ANBZ: torvalds#571

commit 1751fc1 upstream.

If the file type changes back to being a regular file on the server
between the failed OPEN and our LOOKUP, then we need to re-run the OPEN.

Fixes: 0dd2b47 ("nfs: implement i_op->atomic_open()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Hongnan Li <hongnan.li@linux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>

fs/nfs/dir.c

@@ -1631,12 +1631,17 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 		if ((lookup_flags & LOOKUP_DIRECTORY) && inode &&
 		    !S_ISDIR(inode->i_mode))
 			res = ERR_PTR(-ENOTDIR);
+		else if (inode && S_ISREG(inode->i_mode))
+			res = ERR_PTR(-EOPENSTALE);
 	} else if (!IS_ERR(res)) {
 		inode = d_inode(res);
 		if ((lookup_flags & LOOKUP_DIRECTORY) && inode &&
 		    !S_ISDIR(inode->i_mode)) {
 			dput(res);
 			res = ERR_PTR(-ENOTDIR);
+		} else if (inode && S_ISREG(inode->i_mode)) {
+			dput(res);
+			res = ERR_PTR(-EOPENSTALE);
 		}
 	}
 	if (switched) {