linux-kernel - Re: [PATCH 2/2] perf/x86/amd: Don't allow pre-emption in amd_pmu_lbr

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Date:   Tue, 24 Oct 2023 18:34:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sandipan Das <sandipan.das@....com>,
        "H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-pm@...r.kernel.org, rafael@...nel.org,
        pavel@....cz, linux-perf-users@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 2/2] perf/x86/amd: Don't allow pre-emption in
 amd_pmu_lbr_reset()

On Tue, Oct 24, 2023 at 06:30:38PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 24, 2023 at 11:04:06AM -0500, Mario Limonciello wrote:
> 
> > > IIRC this is the hotplug thread running a teardown function on that CPU
> > > itself. It being a strict per-cpu thread should not trip
> > > smp_processor_id() wanrs.
> > > 
> > 
> > BUG: using smp_processor_id() in preemptible [00000000] code: rtcwake/2960
> > caller is amd_pmu_lbr_reset+0x19/0xc0
> > CPU: 104 PID: 2960 Comm: rtcwake Not tainted 6.6.0-rc6-00002-g3e2c7f3ac51f
> 
> Very much not the cpuhp/%u thread :/, let me try and figure out how that
> happens.

Uhh, my bad, these are the PREPARE/DEAD handlers, they run before online
and after dying. The CPU is completely dead. Running lbr_reset() here
makes no sense.

Did that want to be in amd_pmu_cpu_dying() ?

> 
> > #1025
> > Call Trace:
> >  <TASK>
> >  dump_stack_lvl+0x44/0x60
> >  check_preemption_disabled+0xce/0xf0
> >  ? __pfx_x86_pmu_dead_cpu+0x10/0x10
> >  amd_pmu_lbr_reset+0x19/0xc0
> >  ? __pfx_x86_pmu_dead_cpu+0x10/0x10
> >  amd_pmu_cpu_reset.constprop.0+0x51/0x60
> >  amd_pmu_cpu_dead+0x3e/0x90
> >  x86_pmu_dead_cpu+0x13/0x20
> >  cpuhp_invoke_callback+0x169/0x4b0
> >  ? __pfx_virtnet_cpu_dead+0x10/0x10
> >  __cpuhp_invoke_callback_range+0x76/0xe0
> >  _cpu_down+0x112/0x270
> >  freeze_secondary_cpus+0x8e/0x280