linux-kernel - Re: [PATCHv2 2/2] arm64: cpufeature: use static_branch_enable

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Date:   Fri, 28 Apr 2017 11:07:29 +0100
From:   Will Deacon <will.deacon@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     catalin.marinas@....com, tglx@...utronix.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bigeasy@...utronix.de, jbaron@...mai.com, peterz@...radead.org,
        rostedt@...dmis.org, suzuki.poulose@....com
Subject: Re: [PATCHv2 2/2] arm64: cpufeature: use
 static_branch_enable_cpuslocked()

On Fri, Apr 28, 2017 at 11:02:30AM +0100, Mark Rutland wrote:
> On Thu, Apr 27, 2017 at 07:01:04PM +0100, Will Deacon wrote:
> > On Thu, Apr 27, 2017 at 06:44:37PM +0100, Mark Rutland wrote:
> > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> > > index f6cc67e..379ad8d 100644
> > > --- a/arch/arm64/kernel/cpu_errata.c
> > > +++ b/arch/arm64/kernel/cpu_errata.c
> > > @@ -175,9 +175,20 @@ void verify_local_cpu_errata_workarounds(void)
> > >  		}
> > >  }
> > >  
> > > -void update_cpu_errata_workarounds(void)
> > > +/*
> > > + * Secondary CPUs are booted with the waker holding the
> > > + * CPU hotplug lock, hence we don't need to lock it here again.
> > > + */
> > > +void update_secondary_cpu_errata_workarounds(void)
> > > +{
> > > +	update_cpu_capabilities(arm64_errata, "enabling workaround for");
> > > +}
> > > +
> > > +void update_boot_cpu_errata_workarounds(void)
> > >  {
> > > +	get_online_cpus();
> > >  	update_cpu_capabilities(arm64_errata, "enabling workaround for");
> > > +	put_online_cpus();
> > >  }
> > 
> > These functions seem to have unhelpful names, especially when compared to
> > the naming scheme used by the core code. I'd prefer to have:
> > 
> > update_cpu_errata_workarounds: just calls update_cpu_capabilities
> > 
> > update_cpu_errata_workarounds_cpuslocked: does get_online_cpus(), then calls
> > update_cpu_errata_workarounds, then does put_online_cpus();
> 
> That's the opposite polarity to the other _cpuslocked functions, where
> _cpuslocked means that the lock is already held (and should not be taken
> by the _cpuslocked function itself.
> 
> So I'll make those changes, but I'll swap that so:
> update_cpu_errata_workarounds() does:
> 
>   get_online_cpus()
>   update_cpu_errata_workarounds_cpuslocked()
>   put_online_cpus()
> 
> > With that change:
> > 
> > Acked-by: Will Deacon <will.deacon@....com>
> 
> I assume that will stand with the above change. Please shout if not!

Haha, yes, I got it downside-up. Thanks for working out what I meant.

Will