ceph: fail the open_by_handle_at() if the dentry is being unlinked

When unlinking a file the kclient will send a unlink request to MDS
by holding the dentry reference, and then the MDS will return 2 replies,
which are unsafe reply and a deferred safe reply.

After the unsafe reply received the kernel will return and succeed
the unlink request to user space apps.

Only when the safe reply received the dentry's reference will be
released. Or the dentry will only be unhashed from dcache. But when
the open_by_handle_at() begins to open the unlinked files it will
succeed.

The inode->i_count couldn't be used to check whether the inode is
opened or not.

Link: https://tracker.ceph.com/issues/56524
Signed-off-by: Xiubo Li <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Reviewed-by: Luís Henriques <[email protected]>
Tested-by: Luís Henriques <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>

Author: lxbsz

fs/ceph/export.c

@@ -181,6 +181,7 @@ struct inode *ceph_lookup_inode(struct super_block *sb, u64 ino)
 static struct dentry *__fh_to_dentry(struct super_block *sb, u64 ino)
 {
 	struct inode *inode = __lookup_inode(sb, ino);
+	struct ceph_inode_info *ci = ceph_inode(inode);
 	int err;
 
 	if (IS_ERR(inode))
@@ -192,7 +193,7 @@ static struct dentry *__fh_to_dentry(struct super_block *sb, u64 ino)
 		return ERR_PTR(err);
 	}
 	/* -ESTALE if inode as been unlinked and no file is open */
-	if ((inode->i_nlink == 0) && (atomic_read(&inode->i_count) == 1)) {
+	if ((inode->i_nlink == 0) && !__ceph_is_file_opened(ci)) {
 		iput(inode);
 		return ERR_PTR(-ESTALE);
 	}