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Date: Sun, 12 May 2013 23:36:55 -0400
From: "Theodore Ts'o" <tytso@mit.edu>
To: Tony Luck <tony.luck@gmail.com>
Cc: eunb.song@samsung.com, Dmitry Monakhov <dmonakhov@openvz.org>,
        "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
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Subject: Re: EXT4 panic at jbd2_journal_put_journal_head() in 3.9+
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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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