linux-kernel - Re: [tip:perf/core] perf/x86: Tone down kernel messages when the PMU check fails in a virtual environment

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Date:	Tue, 7 Oct 2014 14:47:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, wei@...hat.com, acme@...nel.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/x86:  Tone down kernel messages when the
 PMU check fails in a virtual environment

On Mon, Oct 06, 2014 at 02:10:23PM -0700, Andy Lutomirski wrote:
> On 10/02/2014 10:28 PM, tip-bot for Wei Huang wrote:
> >  msr_fail:
> >  	printk(KERN_CONT "Broken PMU hardware detected, using software events only.\n");
> > -	printk(KERN_ERR "Failed to access perfctr msr (MSR %x is %Lx)\n", reg, val_new);
> > +	printk(boot_cpu_has(X86_FEATURE_HYPERVISOR) ? KERN_INFO : KERN_ERR
> > +	       "Failed to access perfctr msr (MSR %x is %Lx)\n", reg, val_new);
> >  
> 
> This is bogus.  String concatenation doesn't work like that.
> 
> Try "%sFailed...", boot_cpu_has(X86_FEATURE_HYPERVISOR) ? KERN_ERR :
> KERN_INFO), etc.

Haha, indeed. The hypervisor message is empty in this case. Wei, test
this much? ;-)

---
Subject: perf: Fix bogus kernel printk

Andy spotted the fail in what was intended as a conditional printk
level.

Fixes: cc6cd47e7395 ("perf/x86: Tone down kernel messages when the PMU check fails in a virtual environment")
Reported-by: Andy Lutomirski <luto@...capital.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/cpu/perf_event.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -243,8 +243,9 @@ static bool check_hw_exists(void)
 
 msr_fail:
 	printk(KERN_CONT "Broken PMU hardware detected, using software events only.\n");
-	printk(boot_cpu_has(X86_FEATURE_HYPERVISOR) ? KERN_INFO : KERN_ERR
-	       "Failed to access perfctr msr (MSR %x is %Lx)\n", reg, val_new);
+	printk("%sFailed to access perfctr msr (MSR %x is %Lx)\n",
+		boot_cpu_has(X86_FEATURE_HYPERVISOR) ? KERN_INFO : KERN_ERR,
+		reg, val_new);
 
 	return false;
 }
--
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