linux-kernel - Re: [PATCH v2] kvm: Replace vcpu->swait with rcuwait

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Date:   Mon, 20 Apr 2020 14:50:14 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Marc Zyngier <maz@...nel.org>, tglx@...utronix.de,
        kvm@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>,
        peterz@...radead.org, torvalds@...ux-foundation.org,
        bigeasy@...utronix.de, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, linux-mips@...r.kernel.org,
        Paul Mackerras <paulus@...abs.org>, joel@...lfernandes.org,
        will@...nel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2] kvm: Replace vcpu->swait with rcuwait

On Mon, 20 Apr 2020, Paolo Bonzini wrote:

>On 20/04/20 22:56, Davidlohr Bueso wrote:
>> On Mon, 20 Apr 2020, Marc Zyngier wrote:
>>
>>> This looks like a change in the semantics of the tracepoint. Before this
>>> change, 'waited' would have been true if the vcpu waited at all. Here,
>>> you'd
>>> have false if it has been interrupted by a signal, even if the vcpu
>>> has waited
>>> for a period of time.
>>
>> Hmm but sleeps are now uninterruptible as we're using TASK_IDLE.
>
>Hold on, does that mean that you can't anymore send a signal in order to
>kick a thread out of KVM_RUN?  Or am I just misunderstanding?

Considering that the return value of the interruptible wait is not
checked, I would not think this breaks KVM_RUN.

Thanks,
Davidlohr