Re: [PATCH] KVM: selftests: Always run vCPU thread with blocked SIG_IPI

[Paolo Bonzini]

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@xxxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> >
> > Yes, indeed better! :)
> >
> > Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
>
> 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.

Paolo

  From that pov I slightly prefer the old patch.  However
> not a big deal so far as only dirty ring uses SIG_IPI, so there's always ring
> full which will just delay the kick. It's just we need to remember this when we
> extend IPI to non-dirty-ring tests as the kick is prone to be lost then.
>
> Thanks,