linux-ext4 - Re: [PATCH] vfs: avoid hang caused by attempting to rmdir an invalid file system

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Date:	Tue, 29 May 2012 21:50:19 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ted Ts'o <tytso@....edu>
Cc:	Andreas Dilger <adilger@...ger.ca>, linux-fsdevel@...r.kernel.org,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	viro@...IV.linux.org.uk, sami.liedes@....fi
Subject: Re: [PATCH] vfs: avoid hang caused by attempting to rmdir an
 invalid file system

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.

								Honza

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