linux-kernel - Re: EXT4 panic at jbd2_journal_put_journal

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Message-ID: <20130513033655.GE25996@thunk.org>
Date:	Sun, 12 May 2013 23:36:55 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Tony Luck <tony.luck@...il.com>
Cc:	eunb.song@...sung.com, 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>
Subject: Re: EXT4 panic at jbd2_journal_put_journal_head() in 3.9+

On Sun, May 12, 2013 at 08:11:59PM -0700, Tony Luck wrote:
> 
> My best guess as to why this commit causes problems is that there are places
> where updates to individual fields in this structure used to be independent
> because they were to whole words.  Now we have bitfileds there are races
> between access to different fields in the same word.

Yeah, except we access the fields while holding a lock.... wait a
minute.  We're using bit_spinlocks().... and am I missing something?

Where are the barrier statements to prevent the CPU or the compiler
from reordering statements around bit_spin_lock()?  But if that's the
problem, I would have expected lots of other things to be broken.

	   	      	       	       	     - Ted
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