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Date:   Mon, 29 Mar 2021 13:50:18 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Marco Elver <elver@google.com>
Cc:     alexander.shishkin@linux.intel.com, acme@kernel.org,
        mingo@redhat.com, jolsa@redhat.com, mark.rutland@arm.com,
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        viro@zeniv.linux.org.uk, arnd@arndb.de, christian@brauner.io,
        dvyukov@google.com, jannh@google.com, axboe@kernel.dk,
        mascasa@google.com, pcc@google.com, irogers@google.com,
        kasan-dev@googlegroups.com, linux-arch@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        x86@kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 01/11] perf: Rework perf_event_exit_event()
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On Thu, Mar 25, 2021 at 08:10:51PM +0100, Marco Elver wrote:

> and therefore synthesized this fix on top:
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 57de8d436efd..e77294c7e654 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -12400,7 +12400,7 @@ static void sync_child_event(struct perf_event *child_event)
>  	if (child_event->attr.inherit_stat) {
>  		struct task_struct *task = child_event->ctx->task;
>  
> -		if (task)
> +		if (task && task != TASK_TOMBSTONE)
>  			perf_event_read_event(child_event, task);
>  	}
>  
> which fixes the problem. My guess is that the parent and child are both
> racing to exit?
> 
> Does that make any sense?

Yes, I think it does. ACK