fs/9p: Always ask new inode in lookup for cache mode disabled

commit 73f50717 upstream.

This make sure we don't end up reusing the unlinked inode object.
The ideal way is to use inode i_generation. But i_generation is
not available in userspace always.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/9p/vfs_inode.c

@@ -799,6 +799,7 @@ static int v9fs_vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 				      struct nameidata *nameidata)
 {
+	struct dentry *res;
 	struct super_block *sb;
 	struct v9fs_session_info *v9ses;
 	struct p9_fid *dfid, *fid;
@@ -830,22 +831,35 @@ struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 
 		return ERR_PTR(result);
 	}
-
+	/*
+	 * Make sure we don't use a wrong inode due to parallel
+	 * unlink. For cached mode create calls request for new
+	 * inode. But with cache disabled, lookup should do this.
+	 */
+	if (v9ses->cache)
 		inode = v9fs_get_inode_from_fid(v9ses, fid, dir->i_sb);
+	else
+		inode = v9fs_get_new_inode_from_fid(v9ses, fid, dir->i_sb);
 	if (IS_ERR(inode)) {
 		result = PTR_ERR(inode);
 		inode = NULL;
 		goto error;
 	}
-
 	result = v9fs_fid_add(dentry, fid);
 	if (result < 0)
 		goto error_iput;
-
 inst_out:
-	d_add(dentry, inode);
-	return NULL;
-
+	/*
+	 * If we had a rename on the server and a parallel lookup
+	 * for the new name, then make sure we instantiate with
+	 * the new name. ie look up for a/b, while on server somebody
+	 * moved b under k and client parallely did a lookup for
+	 * k/b.
+	 */
+	res = d_materialise_unique(dentry, inode);
+	if (!IS_ERR(res))
+		return res;
+	result = PTR_ERR(res);
 error_iput:
 	iput(inode);
 error: