linux-kernel - Re: Re: Re: EXT4 panic at jbd2_journal_put_journal

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Message-ID: <87fvxrxeuh.fsf@openvz.org>
Date:	Mon, 13 May 2013 16:07:50 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	Zheng Liu <gnehzuil.liu@...il.com>,
	EUNBONG SONG <eunb.song@...sung.com>
Cc:	Tony Luck <tony.luck@...il.com>, Theodore Ts'o <tytso@....edu>,
	"linux-ext4\@vger.kernel.org" <linux-ext4@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Re: Re: EXT4 panic at jbd2_journal_put_journal_head() in 3.9+

On Mon, 13 May 2013 19:26:34 +0800, Zheng Liu <gnehzuil.liu@...il.com> wrote:
> On Mon, May 13, 2013 at 09:53:25AM +0000, EUNBONG SONG wrote:
> > 
> > 
> > > Hi all,
> > 
> > > First of all I couldn't reproduce this regression in my sand box.  So
> > > the following speculation is only my guess.  I suspect that the commit
> > > (ae4647fb) isn't root cause.  It just uncover a potential bug that has
> > > been there for a long time.  I look at the code, and found two
> > > suspicious stuff in jbd2.  The first one is in do_get_write_access().
> > > In this function we forgot to lock bh state when we check b_jlist ==
> > > BJ_Shadow.  I generate a patch to fix it, and I really think it is the
> > > root cause.  Further, in __journal_remove_journal_head() we check
> > > b_jlist == BJ_None.  But, when this function is called, bh state won't
> > > be locked sometimes.  So I suspect this is why we hit a BUG in
> > > jbd2_journal_put_journal_head().  But I don't have a good solution to
> > > fix this until now because I don't know whether we need to lock bh state
> > > here, or maybe we should remove this assertation.
> > >
> > > So, generally, Tony, Eunbong, could you please try the following patch?
> > >
> > > Thanks in advance,
> > >                                                 - Zheng
> > 
> > 
> > Hi, I tested your patch. Unfortunately, the same problem was reproduced.
> > Thanks.
> 
> Thanks for trying this patch.  Could you please repost the dmesg log for
> me?  I want to make sure whether the second suspicious stuff causes this
> regression or not.  Further, that would be great if you could try to
> comment this line as the following?
AFAIK  following assertion was triggered jh->b_transaction != NULL
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 886ec2f..a9e3779 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -2453,7 +2453,7 @@ static void __journal_remove_journal_head(struct
> buffer_head *bh)
>         J_ASSERT_JH(jh, jh->b_transaction == NULL);
>         J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
>         J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
> -       J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
> +       /*J_ASSERT_JH(jh, jh->b_jlist == BJ_None);*/
>         J_ASSERT_BH(bh, buffer_jbd(bh));
>         J_ASSERT_BH(bh, jh2bh(jh) == bh);
>         BUFFER_TRACE(bh, "remove journal_head");
> 
> Really thanks,
>                                                 - Zheng
> --
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