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




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