Re: [tip:perf/core] [perf] da916e96e2: BUG:KASAN:null-ptr-deref_in_put_event

[Oliver Sang]

hi, Peter Zijlstra,

On Mon, Apr 14, 2025 at 09:01:38PM +0200, Peter Zijlstra wrote:
> On Mon, Apr 14, 2025 at 09:59:25AM +0800, kernel test robot wrote:
> > 
> > 
> > Hello,
> > 
> > kernel test robot noticed "BUG:KASAN:null-ptr-deref_in_put_event" on:
> > 
> > commit: da916e96e2dedcb2d40de77a7def833d315b81a6 ("perf: Make perf_pmu_unregister() useable")
> > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git perf/core
> > 
> > [test failed on linux-next/master 29e7bf01ed8033c9a14ed0dc990dfe2736dbcd18]
> > 
> > in testcase: trinity
> > version: trinity-x86_64-ba2360ed-1_20241228
> > with following parameters:
> > 
> > 	runtime: 300s
> > 	group: group-02
> > 	nr_groups: 5
> > 
> > 
> > 
> > config: x86_64-randconfig-078-20250407
> > compiler: clang-20
> > test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> > 
> > (please refer to attached dmesg/kmsg for entire log/backtrace)
> > 
> > 
> > 
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > | Closes: https://lore.kernel.org/oe-lkp/202504131701.941039cd-lkp@xxxxxxxxx
> > 
> 
> Does this help?

yes, below patch fixes the issues we observed for da916e96e2. thanks

Tested-by: kernel test robot <oliver.sang@xxxxxxxxx>

> 
> ---
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2eb9cd5d86a1..528b679aaf7e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5687,7 +5687,7 @@ static void put_event(struct perf_event *event)
>  	_free_event(event);
>  
>  	/* Matches the refcount bump in inherit_event() */
> -	if (parent)
> +	if (parent && parent != EVENT_TOMBSTONE)
>  		put_event(parent);
>  }
>