linux-kernel - Re: [PATCH 2/2] x86, mce: Add persistent MCE event

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Date:	Thu, 22 Mar 2012 12:40:51 +0100
From:	Borislav Petkov <bp@...64.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Borislav Petkov <bp@...64.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86, mce: Add persistent MCE event

On Thu, Mar 22, 2012 at 02:06:29PM +0530, Srivatsa S. Bhat wrote:
> > +err_unwind:
> > +	err = -EINVAL;
> > +	for (--cpu; cpu >= 0; cpu--)
> > +		perf_rm_persistent_on_cpu(cpu, &per_cpu(mce_ev, cpu));
> > +
> 
> 
> *Totally* theoretical question: How do you know that the cpu_online_mask isn't
> sparse? In other words, what if some CPUs weren't booted? Then this for-loop
> wouldn't be very good..
> 
> Oh, now I see that perf_rm_persistent_on_cpu() probably handles that case well..
> So no issues I guess.. ?

Right, this could theoretically come around to bite us in some obscure
cases, so we probably fix it from the get-go.

> (Moreover, we will probably have bigger issues at hand if some CPU didn't
> boot..)
> 
> (The code looked funny, so I thought of pointing it out, whether or not it
> actually is worrisome. Sorry for the noise, if any).

Right, no, thanks for pointing it out.

I'll probably do something like the following:

	for (--cpu; cpu >= 0; cpu--)
		if (cpu_online(cpu))
			perf_rm_persistent_on_cpu(cpu, &per_cpu(mce_ev, cpu));

to be on the safe side from that perspective.

Thanks.

-- 
Regards/Gruss,
Boris.

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