From: Josef Bacik <josef@redhat.com>
Subject: Re: [PATCH] Ext4: wait for log to commit when putting super
Date: Mon, 7 Dec 2009 15:31:56 -0500
Message-ID: <20091207203156.GC8558@localhost.localdomain>
References: <20091207200924.GB8558@localhost.localdomain> <4B1D64ED.5060403@redhat.com>
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Cc: Josef Bacik <josef@redhat.com>, linux-ext4@vger.kernel.org
To: Eric Sandeen <sandeen@redhat.com>
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In-Reply-To: <4B1D64ED.5060403@redhat.com>
Sender: linux-ext4-owner@vger.kernel.org

On Mon, Dec 07, 2009 at 02:26:21PM -0600, Eric Sandeen wrote:
> Josef Bacik wrote:
> > There is a problem where a transaction will be committing while we're unmounting
> > the filesystem and you will get a panic because EXT4_SB(sb)->s_group_info has
> > been kfree'ed in ext4_put_super.  The commit code does the callback for the
> > mballoc stuff to release free'ed blocks in the transaction and panic's trying to
> > access s_group_info.  The fix is to wait for the transaction to finish
> > committing before we start cleaning up the mballoc stuff.  This patch hasn't
> > been tested yet, but its an obvious fix.
> 
> Hm, doesn't jbd2_journal_destroy already do that, but we just
> call it -after- we've done ext4_mb_release which leads to freeing
> EXT4_SB(sb)->s_group_info ?
> 
> Can we just do jbd2_journal_destroy() earlier before we tear
> down things it may depend on?
> 

That seems reasonable.  We do

        ext4_release_system_zone(sb);
        ext4_mb_release(sb);
        ext4_ext_release(sb);
        ext4_xattr_put_super(sb);

before the journal_destroy, and all thats doing is cleaning up our internal
stuff.  If we want to keep it close to what ext3 does we can just move

        ext4_release_system_zone(sb);
        ext4_mb_release(sb);
        ext4_ext_release(sb);

under the journal_destroy or just move the journal destroy above all of that
stuff.  Whichever you prefer.  Thanks,

Josef