linux-kernel - Re: [PATCH] KVM: selftests: Always run vCPU thread with blocked SIG

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Date:   Tue, 20 Apr 2021 12:58:34 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] KVM: selftests: Always run vCPU thread with blocked
 SIG_IPI

On Tue, Apr 20, 2021 at 06:24:50PM +0200, Paolo Bonzini wrote:
> On 20/04/21 17:32, Peter Xu wrote:
> > On Tue, Apr 20, 2021 at 10:37:39AM -0400, Peter Xu wrote:
> > > On Tue, Apr 20, 2021 at 04:16:14AM -0400, Paolo Bonzini wrote:
> > > > The main thread could start to send SIG_IPI at any time, even before signal
> > > > blocked on vcpu thread.  Therefore, start the vcpu thread with the signal
> > > > blocked.
> > > > 
> > > > Without this patch, on very busy cores the dirty_log_test could fail directly
> > > > on receiving a SIGUSR1 without a handler (when vcpu runs far slower than main).
> > > > 
> > > > Reported-by: Peter Xu <peterx@...hat.com>
> > > > Cc: stable@...r.kernel.org
> > > > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > > 
> > > Yes, indeed better! :)
> > > 
> > > Reviewed-by: Peter Xu <peterx@...hat.com>
> > 
> > I just remembered one thing: this will avoid program quits, but still we'll get
> > the signal missing.
> 
> In what sense the signal will be missing?  As long as the thread exists, the
> signal will be accepted (but not delivered because it is blocked); it will
> then be delivered on the first KVM_RUN.

Ah right..  Thanks,

-- 
Peter Xu