linux-kernel - Re: [tip:perf/core] [perf] da916e96e2: BUG:KASAN:null-ptr-deref_in_put

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Message-ID: <20250416084610.GI4031@noisy.programming.kicks-ass.net>
Date: Wed, 16 Apr 2025 10:46:10 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: James Clark <james.clark@...aro.org>
Cc: Oliver Sang <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
	lkp@...el.com, linux-kernel@...r.kernel.org, x86@...nel.org,
	Ravi Bangoria <ravi.bangoria@....com>,
	linux-perf-users@...r.kernel.org,
	Mark Rutland <mark.rutland@....com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [tip:perf/core] [perf] da916e96e2:
 BUG:KASAN:null-ptr-deref_in_put_event

On Tue, Apr 15, 2025 at 04:52:56PM +0100, James Clark wrote:
> Unrelated to the pointer deref issue, I'm also seeing perf stat not working
> due to this commit. And that's both with and without this fixup:
> 
>  -> perf stat -- true
> 
>  Performance counter stats for 'true':
> 
>      <not counted> msec task-clock
> 
>      <not counted>      context-switches
> 
>      <not counted>      cpu-migrations
> 
>      <not counted>      page-faults
> 
>      <not counted>      armv8_cortex_a53/instructions/
> 
>      <not counted>      armv8_cortex_a57/instructions/
> 
>      <not counted>      armv8_cortex_a53/cycles/
> 
>      <not counted>      armv8_cortex_a57/cycles/
> 
>      <not counted>      armv8_cortex_a53/branches/
> 
>      <not counted>      armv8_cortex_a53/branch-misses/
> 
>      <not counted>      armv8_cortex_a57/branch-misses/
> 
> 
>        0.074139992 seconds time elapsed
> 
>        0.000000000 seconds user
>        0.054797000 seconds sys
> 
> Didn't look into it more other than bisecting it to this commit, but I can
> dig more unless the issue is obvious. This is on Arm big.LITTLE, although I
> didn't test it elsewhere so I'm not sure if that's relevant or not.

I can reproduce on x86 alderlake (first machine I tried), so let me go
have a quick poke.