linux-kernel - Re: [PATCH] perf/arm-cmn: Fail DTC counter allocation correctly

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Date:   Mon, 11 Dec 2023 18:21:34 -0800 (PST)
From:   Ilkka Koskinen <ilkka@...amperecomputing.com>
To:     Robin Murphy <robin.murphy@....com>
cc:     will@...nel.org, mark.rutland@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        jeremy.linton@....com, ilkka@...amperecomputing.com,
        renyu.zj@...ux.alibaba.com
Subject: Re: [PATCH] perf/arm-cmn: Fail DTC counter allocation correctly


On Mon, 11 Dec 2023, Robin Murphy wrote:
> Calling arm_cmn_event_clear() before all DTC indices are allocated is
> wrong, and can lead to arm_cmn_event_add() erroneously clearing live
> counters from full DTCs where allocation fails. Since the DTC counters
> are only updated by arm_cmn_init_counter() after all DTC and DTM
> allocations succeed, nothing actually needs cleaning up in this case
> anyway, and it should just return directly as it did before.
>
> Fixes: 7633ec2c262f ("perf/arm-cmn: Rework DTC counters (again)")
> Signed-off-by: Robin Murphy <robin.murphy@....com>

That's a good catch.

     Reviewed-by: Ilkka Koskinen <ilkka@...amperecomputing.com>

Cheers, Ilkka

> ---
> drivers/perf/arm-cmn.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index 86d970e74129..c584165b13ba 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -1816,7 +1816,7 @@ static int arm_cmn_event_add(struct perf_event *event, int flags)
> 			idx = 0;
> 			while (cmn->dtc[j].counters[idx])
> 				if (++idx == CMN_DT_NUM_COUNTERS)
> -					goto free_dtms;
> +					return -ENOSPC;
> 		}
> 		hw->dtc_idx[j] = idx;
> 	}
> -- 
> 2.39.2.101.g768bb238c484.dirty
>
>