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

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Message-ID: <20140221231833.GC12830@htj.dyndns.org>
Date:	Fri, 21 Feb 2014 18:18:33 -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

On Fri, Feb 21, 2014 at 06:01:29PM -0500, Peter Hurley wrote:
> smp_mb__after_unlock_lock() is only for ordering memory operations
> between two spin-locked sections on either the same lock or by
> the same task/cpu. Like:
> 
>    i = 1
>    spin_unlock(lock1)
>    spin_lock(lock2)
>    smp_mb__after_unlock_lock()
>    j = 1
> 
> This guarantees that the store to j happens after the store to i.
> Without it, a cpu can
> 
>    spin_lock(lock2)
>    j = 1
>    i = 1
>    spin_unlock(lock1)

Hmmm?  I'm pretty sure that's a full barrier.  Local processor is
always in order (w.r.t. the compiler).

Thanks.

-- 
tejun
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