ceph: fix memory leak in ceph_readdir when note_last_dentry returns error

Reset the last_readdir at the same time, and add a comment explaining
why we don't free last_readdir when dir_emit returns false.
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/dir.c

@@ -478,8 +478,11 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
 					2 : (fpos_off(rde->offset) + 1);
 			err = note_last_dentry(dfi, rde->name, rde->name_len,
 					       next_offset);
-			if (err)
+			if (err) {
+				ceph_mdsc_put_request(dfi->last_readdir);
+				dfi->last_readdir = NULL;
 				return err;
+			}
 		} else if (req->r_reply_info.dir_end) {
 			dfi->next_offset = 2;
 			/* keep last name */
@@ -520,6 +523,12 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
 		if (!dir_emit(ctx, rde->name, rde->name_len,
 			      ceph_present_ino(inode->i_sb, le64_to_cpu(rde->inode.in->ino)),
 			      le32_to_cpu(rde->inode.in->mode) >> 12)) {
+			/*
+			 * NOTE: Here no need to put the 'dfi->last_readdir',
+			 * because when dir_emit stops us it's most likely
+			 * doesn't have enough memory, etc. So for next readdir
+			 * it will continue.
+			 */
 			dout("filldir stopping us...\n");
 			return 0;
 		}