linux-kernel - Re: spin_lock implicit/explicit memory barrier

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Message-ID: <20160811081139.GT30192@twins.programming.kicks-ass.net>
Date:	Thu, 11 Aug 2016 10:11:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Susanne Spraul <1vier1@....de>, parri.andrea@...il.com
Subject: Re: spin_lock implicit/explicit memory barrier

On Wed, Aug 10, 2016 at 04:29:22PM -0700, Davidlohr Bueso wrote:

> (1) As Manfred suggested, have a patch 1 that fixes the race against mainline
> with the redundant smp_rmb, then apply a second patch that gets rid of it
> for mainline, but only backport the original patch 1 down to 3.12.

I have not followed the thread closely, but this seems like the best
option. Esp. since 726328d92a42 ("locking/spinlock, arch: Update and fix
spin_unlock_wait() implementations") is incomplete, it relies on at
least 6262db7c088b ("powerpc/spinlock: Fix spin_unlock_wait()") to sort
PPC.