linux-kernel - Re: [PATCH v3 01/11] perf: Rework perf_event_exit

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Date:   Mon, 29 Mar 2021 13:50:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     alexander.shishkin@...ux.intel.com, acme@...nel.org,
        mingo@...hat.com, jolsa@...hat.com, mark.rutland@....com,
        namhyung@...nel.org, tglx@...utronix.de, glider@...gle.com,
        viro@...iv.linux.org.uk, arnd@...db.de, christian@...uner.io,
        dvyukov@...gle.com, jannh@...gle.com, axboe@...nel.dk,
        mascasa@...gle.com, pcc@...gle.com, irogers@...gle.com,
        kasan-dev@...glegroups.com, linux-arch@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 01/11] perf: Rework perf_event_exit_event()

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