linux-kernel - Re: [PATCH v3 7/7] perf: Make perf_pmu

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Message-ID: <2d101164-724d-490f-b080-b53f99034175@linux.intel.com>
Date: Thu, 17 Apr 2025 16:24:46 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, ravi.bangoria@....com, lucas.demarchi@...el.com,
 linux-kernel@...r.kernel.org, acme@...nel.org, namhyung@...nel.org,
 mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
 irogers@...gle.com, adrian.hunter@...el.com, kan.liang@...ux.intel.com,
 james.clark@...aro.org
Subject: Re: [PATCH v3 7/7] perf: Make perf_pmu_unregister() useable


On 4/17/2025 4:07 PM, Peter Zijlstra wrote:
> On Mon, Apr 14, 2025 at 08:37:07AM +0800, Mi, Dapeng wrote:
>
>> It seems this patch would break the task attached events counting like the
>> below command shows.
>>
> Right, found another report for that yesterday.
>
> ---
> Subject: perf: Fix perf-stat / read()
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed Apr 16 20:50:27 CEST 2025
>
> In the zeal to adjust all event->state checks to include the new
> REVOKED state, one adjustment was made in error. Notably it resulted
> in read() on the perf filedesc to stop working for any state lower
> than ERROR, specifically EXIT.
>
> This leads to problems with (among others) perf-stat, which wants to
> read the counts after a program has finished execution.
>
> Fixes: da916e96e2de ("perf: Make perf_pmu_unregister() useable")
> Reported-by: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
> Reported-by: James Clark <james.clark@...aro.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/77036114-8723-4af9-a068-1d535f4e2e81@linaro.org
> ---
>  kernel/events/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6023,7 +6023,7 @@ __perf_read(struct perf_event *event, ch
>  	 * error state (i.e. because it was pinned but it couldn't be
>  	 * scheduled on to the CPU at some point).
>  	 */
> -	if (event->state <= PERF_EVENT_STATE_ERROR)
> +	if (event->state == PERF_EVENT_STATE_ERROR)
>  		return 0;
>  
>  	if (count < event->read_size)

Good to know it has been fixed. Thanks.