linux-kernel - Re: [patch 2/4] x86/perf/intel/cstate: Sanitize probing

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Date:	Mon, 21 Mar 2016 16:03:46 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	"Liang, Kan" <kan.liang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Borislav Petkov <bp@...e.de>,
	"Andi Kleen (ak@...ux.intel.com)" <ak@...ux.intel.com>
Subject: Re: [patch 2/4] x86/perf/intel/cstate: Sanitize probing

On Mon, 21 Mar 2016, Peter Zijlstra wrote:

> On Mon, Mar 21, 2016 at 02:19:27PM +0000, Liang, Kan wrote:
> 
> > > -	/* Probe the cstate events. */
> > > -	for (i = 0; i < max_event_nr; i++) {
> > > -		if (!msr[i].test(i) || rdmsrl_safe(msr[i].msr, &val))
> > > -			msr[i].attr = NULL;
> > > -	}
> > 
> > I think we need to update msr[i].attr as well.
> > Because in cstate_pmu_event_init we still need it to do check.
> 
> Yeah, this is exploding on all sides.. 

Gah crap. Why did this not explode in my face? Delta patch below.

Thanks,

	tglx

--- a/arch/x86/events/intel/cstate.c
+++ b/arch/x86/events/intel/cstate.c
@@ -553,6 +553,8 @@ static bool __init cstate_probe_msr(cons
 		if (!rdmsrl_safe(msr[bit].msr, &val)) {
 			*attrs++ = &msr[bit].attr->attr.attr;
 			found = true;
+		} else {
+			msr[bit].attr = NULL;
 		}
 	}
 	*attrs = NULL;