linux-ext4 - Re: [PATCH] jbd2: Fix forever sleeping process in do_get_write

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Date:	Sun, 8 May 2011 19:14:49 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Tao Ma <tm@....ma>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] jbd2: Fix forever sleeping process in
 do_get_write_access()

On Thu, May 05, 2011 at 02:10:39PM +0200, Jan Kara wrote:
> In do_get_write_access() we wait on BH_Unshadow bit for buffer to get
> from shadow state. The waking code in journal_commit_transaction() has
> a bug because it does not issue a memory barrier after the buffer is moved
> from the shadow state and before wake_up_bit() is called. Thus a waitqueue
> check can happen before the buffer is actually moved from the shadow state
> and waiting process may never be woken. Fix the problem by issuing proper
> barrier.
> 
> Reported-by: Tao Ma <boyu.mt@...bao.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, I've added this to the ext4 tree.  (Currently in the dev
branch, pending testing.)

					- Ted
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