From: Peter Staubach <staubach@redhat.com>
Subject: Re: [PATCH] return ENOENT from ext3_link when racing with unlink
Date: Tue, 16 Jan 2007 17:01:04 -0500
Message-ID: <45AD4B20.70507@redhat.com>
References: <45ABC572.2070206@redhat.com>
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Cc: linux-kernel Mailing List <linux-kernel@vger.kernel.org>,
	ext4 development <linux-ext4@vger.kernel.org>, dmonakhov@sw.ru,
	alex@clusterfs.com, Al Viro <viro@ftp.linux.org.uk>
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To: Eric Sandeen <sandeen@redhat.com>
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Eric Sandeen wrote:
> An update from the earlier thread, [PATCH] [RFC] remove ext3 inode 
> from orphan list when link and unlink race
>
> I think this is better than the original idea of trying to handle the 
> race;
> I've seen that the orphan inode list can get corrupted, but there may 
> well
> be other implications of the race which haven't yet been exposed.  I 
> think
> it's safer to simply return -ENOENT in this race window, and avoid other
> potential problems.  Anything wrong with this?
>
> Thanks for the comments suggesting this approach in the prior thread.
>
> Thanks,
>
> -Eric
>
> ---
>
> Return -ENOENT from ext[34]_link if we've raced with unlink and
> i_nlink is 0.  Doing otherwise has the potential to corrupt the
> orphan inode list, because we'd wind up with an inode with a
> non-zero link count on the list, and it will never get properly
> cleaned up & removed from the orphan list before it is freed.
>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>
> Index: linux-2.6.19/fs/ext3/namei.c
> ===================================================================
> --- linux-2.6.19.orig/fs/ext3/namei.c
> +++ linux-2.6.19/fs/ext3/namei.c
> @@ -2191,6 +2191,8 @@ static int ext3_link (struct dentry * ol
>
>     if (inode->i_nlink >= EXT3_LINK_MAX)
>         return -EMLINK;
> +    if (inode->i_nlink == 0)
> +        return -ENOENT;
>
> retry:
>     handle = ext3_journal_start(dir, EXT3_DATA_TRANS_BLOCKS(dir->i_sb) +
> Index: linux-2.6.19/fs/ext4/namei.c
> ===================================================================
> --- linux-2.6.19.orig/fs/ext4/namei.c
> +++ linux-2.6.19/fs/ext4/namei.c
> @@ -2189,6 +2189,8 @@ static int ext4_link (struct dentry * ol
>
>     if (inode->i_nlink >= EXT4_LINK_MAX)
>         return -EMLINK;
> +    if (inode->i_nlink == 0)
> +        return -ENOENT;
>
> retry:
>     handle = ext4_journal_start(dir, EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
>

Just out of curosity, what keeps i_nlink from going to 0 immediately
after the new test is executed?

    Thanx...

       ps