linux-kernel - Re: [PATCH] kvm: fix waitqueue_active without memory barrier in virt/kvm/async

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Message-ID: <56179667.8010609@redhat.com>
Date:	Fri, 9 Oct 2015 12:26:47 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Kosuke Tatsukawa <tatsu@...jp.nec.com>
Cc:	Gleb Natapov <gleb@...nel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kvm: fix waitqueue_active without memory barrier in
 virt/kvm/async_pf.c



On 09/10/2015 11:04, Kosuke Tatsukawa wrote:
> smp_store_mb() called from set_current_state(), which is called from
> prepare_to_wait() should prevent reordering such as below from
> happening.  wait_event*() also calls set_current_state() inside.

Ah, I missed that set_current_state has a memory barrier in it.  The
patch is okay, but please expand the comment to say that this memory
barrier pairs with prepare_to_wait's set_current_state().

Paolo
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