linux-kernel - Re: [PATCH v2] perf script: Fix overrun issue for dynamically-allocated pmu type number

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Date:   Wed, 20 Jan 2021 22:50:04 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jin Yao <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        adrian.hunter@...el.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v2] perf script: Fix overrun issue for
 dynamically-allocated pmu type number

On Wed, Dec 09, 2020 at 08:58:28AM +0800, Jin Yao wrote:
> When unpacking the event which is from dynamic pmu, the array
> output[OUTPUT_TYPE_MAX] may be overrun. For example, type number of
> SKL uncore_imc is 10, but OUTPUT_TYPE_MAX is 7 now (OUTPUT_TYPE_MAX =
> PERF_TYPE_MAX + 1).
> 
> /* In builtin-script.c */
> process_event()
> {
>         unsigned int type = output_type(attr->type);
> 
>         if (output[type].fields == 0)
>                 return;
> }
> 
> output[10] is overrun.
> 
> Create a type OUTPUT_TYPE_OTHER for dynamic pmu events, then
> output_type(attr->type) will return OUTPUT_TYPE_OTHER here.
> 
> Note that if PERF_TYPE_MAX ever changed, then there would be a conflict
> between old perf.data files that had a dynamicaliy allocated PMU number
> that would then be the same as a fixed PERF_TYPE.
> 
> Example:
> 
> perf record --switch-events -C 0 -e "{cpu-clock,uncore_imc/data_reads/,uncore_imc/data_writes/}:SD" -a -- sleep 1
> perf script
> 
> Before:
>          swapper     0 [000] 1479253.987551:     277766               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.987797:     246709               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.988127:     329883               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.988273:     146393               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.988523:     249977               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.988877:     354090               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.989023:     145940               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.989383:     359856               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1479253.989523:     140082               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
> 
> After:
>          swapper     0 [000] 1397040.402011:     272384               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1397040.402011:       5396  uncore_imc/data_reads/:
>          swapper     0 [000] 1397040.402011:        967 uncore_imc/data_writes/:
>          swapper     0 [000] 1397040.402259:     249153               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1397040.402259:       7231  uncore_imc/data_reads/:
>          swapper     0 [000] 1397040.402259:       1297 uncore_imc/data_writes/:
>          swapper     0 [000] 1397040.402508:     249108               cpu-clock:  ffffffff9d4ddb6f cpuidle_enter_state+0xdf ([kernel.kallsyms])
>          swapper     0 [000] 1397040.402508:       5333  uncore_imc/data_reads/:
>          swapper     0 [000] 1397040.402508:       1008 uncore_imc/data_writes/:
> 
> Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
> ---
> v2:
>   Remove Fixes tag because this issue has always been here, not caused by
>   1405720d4f26 ("perf script: Add 'synth' event type for synthesized events").
>   No functional change in v2. 

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka