Re: [Qemu-devel] [RFC 03/10] cpus: Introduce async_wait_run_on_cpu()

From: "Alex Bennée" <alex.bennee@linaro.org>
To: Sergey Fedorov <serge.fdrv@gmail.com>
Cc: "alvise rigo" <a.rigo@virtualopensystems.com>,
	"MTTCG Devel" <mttcg@listserver.greensocs.com>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	"Jani Kokkonen" <jani.kokkonen@huawei.com>,
	"Claudio Fontana" <claudio.fontana@huawei.com>,
	"VirtualOpenSystems Technical Team" <tech@virtualopensystems.com>,
	"KONRAD Frédéric" <fred.konrad@greensocs.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Richard Henderson" <rth@twiddle.net>,
	"Emilio G. Cota" <cota@braap.org>,
	"Peter Maydell" <peter.maydell@linaro.org>
Subject: Re: [Qemu-devel] [RFC 03/10] cpus: Introduce async_wait_run_on_cpu()
Date: Wed, 08 Jun 2016 16:20:40 +0100	[thread overview]
Message-ID: <87a8ivhflj.fsf@linaro.org> (raw)
In-Reply-To: <57583182.3090701@gmail.com>

Sergey Fedorov <serge.fdrv@gmail.com> writes:

> On 08/06/16 17:10, alvise rigo wrote:
>> Using run_on_cpu() we might deadlock QEMU if other vCPUs are waiting
>> for the current vCPU. We need to exit from the vCPU loop in order to
>> avoid this.
>
> I see, we could deadlock indeed. Alternatively, we may want fix
> run_on_cpu() to avoid waiting for completion by itself when called from
> CPU loop.

async_safe_run_on_cpu can't deadlock as all vCPUs are suspended (or
waiting) for the work to complete. The tasks are run in strict order so
if you queued async tasks for other vCPUs first you could ensure
everything is in the state you want it when you finally service the
calling vCPU.

>
> Kind regards,
> Sergey

--
Alex Bennée