From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Alex Bennée" <alex.bennee@linaro.org>,
"QEMU Developers" <qemu-devel@nongnu.org>,
"Richard Henderson" <rth@twiddle.net>,
"Emilio G. Cota" <cota@braap.org>
Subject: Re: [Qemu-devel] racing between pause_all_vcpus() and qemu_cpu_stop()
Date: Tue, 2 Oct 2018 11:59:01 +0200 [thread overview]
Message-ID: <59e637ee-2a5a-6256-461a-7c8037e81558@redhat.com> (raw)
In-Reply-To: <CAFEAcA-M_x8oC_1Z5A9Lv3DQ1Z+_vVdyUnaHoBMv4nkJepcBhA@mail.gmail.com>
On 02/10/2018 11:04, Peter Maydell wrote:
> On 2 October 2018 at 09:58, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> First, the reset code should indeed use run_on_cpu (it need not be safe
>> i.e. stop-the-world; just run it in the vCPU thread). It certainly
>> doesn't do this right now.
>
> I don't understand this part. We're resetting the entire world:
> surely we need to stop the entire world first ?
Most of the world is stopped because it only runs with BQL taken. vCPU
isn't, so we ensure it is stopped by: 1) using run_on_cpu to synchronize
with the executed TBs (or KVM_RUN) 2) ensuring the execution loop is
paused after reset, which is the cpu_can_run part that you snipped.
"Safe" CPU work items on the other hand ensure that _no_ vCPU is in the
execution loop, which is overkill here.
Paolo
> (Also, other things use pause_all_vcpus() and hit this race
> condition, like VM suspend and shutdown.)
>
> thanks
> -- PMM
>
next prev parent reply other threads:[~2018-10-02 9:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-01 17:03 [Qemu-devel] racing between pause_all_vcpus() and qemu_cpu_stop() Peter Maydell
2018-10-01 18:12 ` Alex Bennée
2018-10-02 8:01 ` Peter Maydell
2018-10-02 8:58 ` Paolo Bonzini
2018-10-02 9:04 ` Peter Maydell
2018-10-02 9:59 ` Paolo Bonzini [this message]
2018-10-02 10:34 ` Peter Maydell
2018-10-02 16:46 ` Paolo Bonzini
2018-10-02 16:57 ` Peter Maydell
2018-10-02 10:00 ` Alex Bennée
2018-10-02 10:31 ` Peter Maydell
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