linux-kernel - Re: [PATCH 4/4] locking: Introduce smp_cond

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Date:	Thu, 12 Nov 2015 20:33:02 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Boqun Feng <boqun.feng@...il.com>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	corbet@....net, mhocko@...nel.org, dhowells@...hat.com,
	torvalds@...ux-foundation.org, will.deacon@....com,
	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()

On 11/12, Peter Zijlstra wrote:
>
> On Thu, Nov 12, 2015 at 07:38:07PM +0100, Oleg Nesterov wrote:
> > It seems that PPC needs to define smp_mb__before_spinlock() as full mb(),
> > no?
>
> It does:
>
> arch/powerpc/include/asm/barrier.h:#define smp_mb__before_spinlock() smp_mb()

Ah, indeed, thanks.

And given that it also defines smp_mb__after_unlock_lock() as smp_mb(),
I am starting to understand how it can help to avoid the races with
spin_unlock_wait() in (for example) do_exit().

But as Boqun has already mentioned, this means that mb__after_unlock_lock()
has the new meaning which should be documented.

Hmm. And 12d560f4 "Privatize smp_mb__after_unlock_lock()" should be reverted
then ;)

Oleg.

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