From: Peter Zijlstra <peterz@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>,
Gleb Natapov <gleb@kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kvm: fix waitqueue_active without memory barrier in virt/kvm/async_pf.c
Date: Fri, 9 Oct 2015 10:50:40 +0200 [thread overview]
Message-ID: <20151009085040.GZ7520@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <56177EAC.2070601@redhat.com>
On Fri, Oct 09, 2015 at 10:45:32AM +0200, Paolo Bonzini wrote:
> So you need another smp_mb() after prepare_to_wait(). I'm not sure
> if it's needed also for your original tty report, but I think it is
> for https://lkml.org/lkml/2015/10/8/989 ("mei: fix waitqueue_active
> without memory barrier in mei drivers").
>
> I wonder if it makes sense to introduce smp_mb__before_spin_lock()
> and smp_mb__after_spin_unlock(). On x86 the former could be a
> simple compiler barrier, and on s390 both of them could. But that
> should be a separate patch.
Not having actually read or thought about the issue at hand, its
perfectly valid to pair an smp_mb() with either spin_lock() or
spin_unlock().
IOW. MB <-> {ACQUIRE, RELEASE} is a valid pairing.
next prev parent reply other threads:[~2015-10-09 8:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-09 0:35 [PATCH] kvm: fix waitqueue_active without memory barrier in virt/kvm/async_pf.c Kosuke Tatsukawa
2015-10-09 8:45 ` Paolo Bonzini
2015-10-09 8:50 ` Peter Zijlstra [this message]
2015-10-09 10:24 ` Paolo Bonzini
2015-10-09 9:04 ` Kosuke Tatsukawa
2015-10-09 10:26 ` Paolo Bonzini
2015-10-09 12:21 ` Kosuke Tatsukawa
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