linux-kernel - Re: [PATCH 2/2] KVM: selftests: Use getcpu() instead of sched_getcpu() in rseq

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Message-ID: <YvLJUEOcxaZKW0y1@google.com>
Date:   Tue, 9 Aug 2022 20:53:36 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     Florian Weimer <fweimer@...hat.com>, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com, maz@...nel.org,
        oliver.upton@...ux.dev, andrew.jones@...ux.dev,
        mathieu.desnoyers@...icios.com, yihyu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH 2/2] KVM: selftests: Use getcpu() instead of
 sched_getcpu() in rseq_test

On Tue, Aug 09, 2022, Gavin Shan wrote:
> On 8/9/22 5:17 PM, Florian Weimer wrote:
> > * Florian Weimer:
> > 
> > > * Gavin Shan:
> > > 
> > > > sched_getcpu() is glibc dependent and it can simply return the CPU
> > > > ID from the registered rseq information, as Florian Weimer pointed.
> > > > In this case, it's pointless to compare the return value from
> > > > sched_getcpu() and that fetched from the registered rseq information.
> > > > 
> > > > Fix the issue by replacing sched_getcpu() with getcpu(), as Florian
> > > > suggested. The comments are modified accordingly.
> > > 
> > > Note that getcpu was added in glibc 2.29, so perhaps you need to perform
> > > a direct system call?
> > 
> > One more thing: syscall(__NR_getcpu) also has the advantage that it
> > wouldn't have to be changed again if node IDs become available via rseq
> > and getcpu is implemented using that.
> > 
> > Thanks,
> > Florian
> > 
> 
> Thanks, Florian. It makes sense to me to use syscall(__NR_getcpu) in
> next revision. Thanks for your quick review :)

+1, and definitely add a comment to prevent future "cleanup".