From: Josef Bacik <jbacik@fusionio.com>
To: Liu Bo <liub.liubo@gmail.com>
Cc: Josef Bacik <JBacik@fusionio.com>,
"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH] Btrfs: barrier before waitqueue_active
Date: Thu, 2 Aug 2012 08:11:58 -0400 [thread overview]
Message-ID: <20120802121158.GF2263@localhost.localdomain> (raw)
In-Reply-To: <501A5A94.7070307@gmail.com>
On Thu, Aug 02, 2012 at 04:46:44AM -0600, Liu Bo wrote:
> On 08/02/2012 04:25 AM, Josef Bacik wrote:
> > We need an smb_mb() before waitqueue_active to avoid missing wakeups.
> > Before Mitch was hitting a deadlock between the ordered flushers and the
> > transaction commit because the ordered flushers were waiting for more refs
> > and were never woken up, so those smp_mb()'s are the most important.
> > Everything else I added for correctness sake and to avoid getting bitten by
> > this again somewhere else. Thanks,
> >
>
> Hi Josef,
>
> I'll appreciate a lot if you can add some comments for each memory
> barrier, because not everyone knows why it is used here and there. :)
>
I'm not going to add comments to all those places, you need a memory barrier in
places you don't have an implicit barrier before you do waitqueue_active because
you could miss somebody being added to the waitqueue, it's just basic
correctness. Thanks,
Josef
next prev parent reply other threads:[~2012-08-02 12:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-01 20:25 [PATCH] Btrfs: barrier before waitqueue_active Josef Bacik
2012-08-02 0:21 ` Mitch Harder
2012-08-03 14:43 ` Mitch Harder
2012-08-05 9:18 ` Arne Jansen
2012-08-02 10:46 ` Liu Bo
2012-08-02 12:11 ` Josef Bacik [this message]
2012-08-02 13:02 ` David Sterba
2012-08-02 13:01 ` cwillu
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