linux-kernel - Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED

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Message-ID: <20140222143859.GD12830@htj.dyndns.org>
Date:	Sat, 22 Feb 2014 09:38:59 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	laijs@...fujitsu.com, linux-kernel@...r.kernel.org,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	linux1394-devel@...ts.sourceforge.net,
	Chris Boot <bootc@...tc.net>, linux-scsi@...r.kernel.org,
	target-devel@...r.kernel.org
Subject: Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK

Hey,

On Fri, Feb 21, 2014 at 06:46:24PM -0500, Peter Hurley wrote:
> It's a long story but the short version is that
> Documentation/memory-barriers.txt recently was overhauled to reflect
> what cpus actually do and what the different archs actually
> deliver.
> 
> Turns out that unlock + lock is not guaranteed by all archs to be
> a full barrier. Thus the smb_mb__after_unlock_lock().
> 
> This is now all spelled out in memory-barriers.txt under the
> sub-heading "IMPLICIT KERNEL MEMORY BARRIERS".

So, that one is for unlock/lock sequence, not smp_mb__after_unlock().
Urgh... kinda dislike adding smp_rmb() there as it's one of the
barriers which translate to something weighty on most, if not all,
archs.

Thanks.

-- 
tejun
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