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

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Date:   Thu, 26 Nov 2020 15:06:53 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Adrian Hunter <adrian.hunter@...el.com>, acme@...nel.org,
        jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com
Cc:     Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf script: Fix overrun issue for dynamically-allocated
 pmu type number

Hi Adrian,

On 11/26/2020 2:51 PM, Adrian Hunter wrote:
> On 26/11/20 5:24 am, 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/:
>>
>> Fixes: 1405720d4f26 ("perf script: Add 'synth' event type for synthesized events")
> 
> It does not look to me like the problem was introduced by that commit.  Are
> you sure this Fixes tag is correct?
> 

Commit 1405720d4f26 added the change:

@@ -1215,8 +1253,9 @@ static void process_event(struct perf_script *script,
  {
         struct thread *thread = al->thread;
         struct perf_event_attr *attr = &evsel->attr;
+       unsigned int type = output_type(attr->type);

-       if (output[attr->type].fields == 0)
+       if (output[type].fields == 0)
                 return;

But of course, we can also say the original "output[attr->type].fields" introduced the issue, I'm 
not sure. Maybe Arnaldo can help to make the decision. :)

Thanks
Jin Yao