linux-kernel - Re: [PATCH v2 24/24] perf: Make perf_pmu

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Message-ID: <3c4ee384-6681-4de3-82e7-64022438e162@amd.com>
Date: Wed, 19 Feb 2025 20:00:57 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: "mingo@...nel.org" <mingo@...nel.org>,
 "lucas.demarchi@...el.com" <lucas.demarchi@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "willy@...radead.org" <willy@...radead.org>,
 "acme@...nel.org" <acme@...nel.org>,
 "namhyung@...nel.org" <namhyung@...nel.org>,
 "mark.rutland@....com" <mark.rutland@....com>,
 "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
 "jolsa@...nel.org" <jolsa@...nel.org>,
 "irogers@...gle.com" <irogers@...gle.com>,
 "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
 "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v2 24/24] perf: Make perf_pmu_unregister() useable

>>>>> Apparently not, it ends up with:
>>>>>
>>>>>   ------------[ cut here ]------------
>>>>>   WARNING: CPU: 145 PID: 5459 at kernel/events/core.c:281 event_function+0xd2/0xf0
>>>>>   WARNING: CPU: 145 PID: 5459 at kernel/events/core.c:286 event_function+0xd6/0xf0
>>>>
>>>>>    remote_function+0x4f/0x70
>>>>>    generic_exec_single+0x7f/0x160
>>>>>    smp_call_function_single+0x110/0x160
>>>>>    event_function_call+0x98/0x1d0
>>>>>    _perf_event_disable+0x41/0x70
>>>>>    perf_event_for_each_child+0x40/0x90
>>>>>    _perf_ioctl+0xac/0xb00
>>>>>    perf_ioctl+0x45/0x80
>>>>
>>>> Took me a long while trying to blame this on the 'event->parent =
>>>> NULL;', but AFAICT this is a new, unrelated issue.
>>>>
>>>> What I think happens is this perf_ioctl(DISABLE) vs pmu_detach_events()
>>>> race, where the crux is that perf_ioctl() path does not take
>>>> event2->mutex which allows the following interleave:
>>>
>>> This one was only with perf_fuzzer, so pmu_detach_events() code path was
>>> not invoked.
>>
>> I think the issue is, unaccount_event() gets called for the child event
>> after the child is detached. Since event->parent is NULL, unaccount_event()
>> abruptly corrupts the perf_sched_work.
> 
> A different manifestation of the same underlying issue (perf_sched_work
> is getting corrupted because of event->parent = NULL):

Duh! I meant perf_sched_events gets corrupted by invoking perf_sched_work.

Thanks,
Ravi