When a directory hierarchy is corrupted (e. g. due to a bit flip on the media),
it can happen that it contains loops of directories. That creates possibilities
for deadlock when locking directories.

Fix the problem by checking in d_splice_alias() that when we splice a
directory, it does not have any other connected alias.

Reported-by: Sami Liedes <redacted>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/dcache.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 4435d8b..ca31a1e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c

@@ -1658,6 +1658,10 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 			d_move(new, dentry);
 			iput(inode);
 		} else {
+			if (unlikely(!list_empty(&inode->i_dentry))) {
+				spin_unlock(&inode->i_lock);
+				return ERR_PTR(-EIO);
+			}
 			/* already taking inode->i_lock, so d_add() by hand */
 			__d_instantiate(dentry, inode);
 			spin_unlock(&inode->i_lock);

-- 
1.7.1