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

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Date:	Thu, 20 Feb 2014 21:13:41 -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 Thu, Feb 20, 2014 at 09:07:27PM -0500, Peter Hurley wrote:
> On 02/20/2014 08:59 PM, Tejun Heo wrote:
> >Hello,
> >
> >On Thu, Feb 20, 2014 at 08:44:46PM -0500, Peter Hurley wrote:
> >>>+static void fw_device_workfn(struct work_struct *work)
> >>>+{
> >>>+	struct fw_device *device = container_of(to_delayed_work(work),
> >>>+						struct fw_device, work);
> >>
> >>I think this needs an smp_rmb() here.
> >
> >The patch is equivalent transformation and the whole thing is
> >guaranteed to have gone through pool->lock.  No explicit rmb
> >necessary.
> 
> The spin_unlock_irq(&pool->lock) only guarantees completion of
> memory operations _before_ the unlock; memory operations which occur
> _after_ the unlock may be speculated before the unlock.
> 
> IOW, unlock is not a memory barrier for operations that occur after.

It's not just unlock.  It's lock / unlock pair on the same lock from
both sides.  Nothing can sip through that.

-- 
tejun
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