From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH 3/3] kvm tools: Make virtio-blk kvm__irq_line thread safe
Date: Fri, 29 Apr 2011 09:55:13 +0300
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Cc: Asias He <asias.hejun@gmail.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Sasha Levin <levinsasha928@gmail.com>,
	Prasad Joshi <prasadjoshi124@gmail.com>, kvm@vger.kernel.org
To: Ingo Molnar <mingo@elte.hu>
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On Fri, Apr 29, 2011 at 9:44 AM, Ingo Molnar <mingo@elte.hu> wrote:
> Hm, this looks a bit strange (the mutex here protects only a kernel call - that
> cannot be right) and there's no explanation why it's needed. Why do
> VIRTIO_BLK_IRQ (== KVM_IRQ_LINE ioctl()) calls have to be covered by the mutex?
>
> A short blurb about expected behavior on SMP and locking rules at the top of
> virtio-blk.c would be nice.

Yes, looks strange. Asias, did you see some bad behavior that this
fixes? The per-device mutexes are there to protect device state. The
assumption here is that KVM handles KVM_IRQ_LINE ioctl() serialization
by titself.