linux-kernel - Re: Re: Re: EXT4 regression caused 4eec7

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Message-ID: <20130513151727.GI400@quack.suse.cz>
Date:	Mon, 13 May 2013 17:17:27 +0200
From:	Jan Kara <jack@...e.cz>
To:	Zheng Liu <gnehzuil.liu@...il.com>
Cc:	Jan Kara <jack@...e.cz>, EUNBONG SONG <eunb.song@...sung.com>,
	Theodore Ts'o <tytso@....edu>,
	Dmitry Monakhov <dmonakhov@...nvz.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>
Subject: Re: Re: Re: EXT4 regression caused 4eec7

On Mon 13-05-13 21:56:43, Zheng Liu wrote:
> On Mon, May 13, 2013 at 03:18:09PM +0200, Jan Kara wrote:
> > On Sun 12-05-13 13:04:59, EUNBONG SONG wrote:
> > > 
> > > 
> > > >> Since at this point it's safer to rollback the change and we can
> > > >> investigate more deeply how to fix it correctly for the next
> > > >> development cycle, this is the patch which I'm testing.
> > > 
> > > >>                     - Ted
> > > 
> > > > Hello, I've tested with your patch. But the same problem was reproduced.
> > > > Currently, I'm trying to git bisect. If i done git bisect, i will let you know.
> > > 
> > > Hi, I've done git bisect. and panic at jbd2_journal_put_journal_head() is caused by 
> > > ae4647fb7654676fc44a97e86eb35f9f06b99f66: "jbd2: reduce journal_head size."
> > > I write just code patch which revert ae4647fb7654676fc44a97e86eb35f9f06b99f66 because
> > > I don't know the root cause. 
> >   This is really strange. I've verified the code and all the places
> > modifying b_jlist or b_modified are holding bh_state lock so we should be
> > safe...
> 
> Hi Jan,
> 
> Could you please take a look at this mail [1].  I don't think we hold
> bh_state lock there.
> 
> 1. http://www.spinics.net/lists/linux-ext4/msg38205.html
  I'll also reply to that thread but: Yes, we don't hold bh_state lock when
reading b_jlist in that one case (that's why I wrote 'modify' and not just
'access' in my previous email). But that's really harmless since we don't
do any complex operations with b_jlist (only get & set) so we either see an
old value or a new one. And that particular use is going away anyway later
in my series.

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