On Tue 29-05-12 21:50:19, Jan Kara wrote:
> On Mon 28-05-12 17:05:11, Ted Tso wrote:
> > On Mon, May 28, 2012 at 02:29:05PM -0600, Andreas Dilger wrote:
> > > This patch is good from the POV of covering all filesystems, and
> > > avoiding the deadlock at the dcache level. It would be possible to
> > > detect this problem in the filesystem itself during lookup, before
> > > the bad link got into the dcache itself. Something like:
> >
> > I like that as a solution for detecting the problem in ext4. As you
> > say, it's still an issue for other file systems, and so the patch I
> > proposed is still probably a good idea for the VFS. But this way ext4
> > (and ext3 when Jan backports it) will be able to detect the problem
> > and mark the file system as being corrupted.
> Actually, I think there's even better way. d_splice_alias() can rather
> easily detect the problem and report it to filesystem. The advantage is
> that the check in d_splice_alias() can catch any "hardlinks" to
> directories, not just self loops. The patch is attached, I also have
> corresponding handling written for ext? filesystems but that's trivial.
> I'll post the whole series to Al to have a look.
And now with the attachment. Sorry.
Honza
>From 0715b656ac88ce1bb62800b14d99ef2e25c26d28 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@xxxxxxx>
Date: Tue, 29 May 2012 21:19:01 +0200
Subject: [PATCH 1/4] vfs: Avoid creation of directory loops for corrupted filesystems
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 <sami.liedes@xxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
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
