linux-ext4 - Re: Ordered mode rewrite patch

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Message-ID: <20080414174722.GG15824@duck.suse.cz>
Date:	Mon, 14 Apr 2008 19:47:22 +0200
From:	Jan Kara <jack@...e.cz>
To:	Josef Bacik <jbacik@...hat.com>
Cc:	Nathan Grennan <jack@...nusx-1.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	linux-ext4@...r.kernel.org
Subject: Re: Ordered mode rewrite patch

  Hi Josef,

On Fri 11-04-08 14:42:58, Josef Bacik wrote:
> On Tue, Apr 08, 2008 at 02:11:49PM +0200, Jan Kara wrote:
> >   Hello,
> > 
> >   attached is a jumbo patch that reverses locking order of transaction
> > start and page lock in ext3 and rewrites handling of ordered data mode in
> > JBD and ext3. Note that the patch will break compilation of ext4 and OCFS2.
> > The patch survives LTP run on my test machine so it shouldn't eat your data
> > immediately but bugs are of course possible...
> >   I'm very interested in any results (both positive and negative) you could
> > get with it :). Thanks for testing it.
> > 
> > 									Honza
> I just hit a problem with your patch.  In journal_destroy() we do a
> iput(journal->j_inode) and then kfree the journal, so when the iput comes back
> into journal_release_jbd_inode we are doing a use after free which in my case
> resulted in a panic.  I was going to fix it but I figure since this is still in
> transit you would have to just rewrite it so I'm not going to attach one, just
> giving you a heads up.  Let me know if my explanation wasn't clear enough.
  Thanks for letting me know. But I don't quite get it:
journal_destroy() does:
        if (journal->j_inode)
                iput(journal->j_inode);
        if (journal->j_revoke)
                journal_destroy_revoke(journal);
        kfree(journal->j_wbuf);
        kfree(journal);
}

  iput() will eventually call generic_forget_inode() which calls
clear_inode() in which we do journal_release_jbd_inode(). But at that
moment journal still exists to I don't see any use after free... But
possibly there could be some other inode in the inode list but which one is
it?

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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