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Message-ID: <ZTf2IxAVPUFq91F4@gmail.com>
Date: Tue, 24 Oct 2023 18:51:47 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Mario Limonciello <mario.limonciello@....com>
Cc: Peter Zijlstra <peterz@...radead.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()
* Ingo Molnar <mingo@...nel.org> wrote:
>
> * Mario Limonciello <mario.limonciello@....com> wrote:
>
> > Fixes a BUG reported during suspend to ram testing.
> >
> > ```
> > [ 478.274752] BUG: using smp_processor_id() in preemptible [00000000] code: rtcwake/2948
> > [ 478.274754] caller is amd_pmu_lbr_reset+0x19/0xc0
> > ```
> >
> > Cc: stable@...r.kernel.org # 6.1+
> > Fixes: ca5b7c0d9621 ("perf/x86/amd/lbr: Add LbrExtV2 branch record support")
> > Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> > ---
> > arch/x86/events/amd/lbr.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c
> > index eb31f850841a..5b98e8c7d8b7 100644
> > --- a/arch/x86/events/amd/lbr.c
> > +++ b/arch/x86/events/amd/lbr.c
> > @@ -321,7 +321,7 @@ int amd_pmu_lbr_hw_config(struct perf_event *event)
> >
> > void amd_pmu_lbr_reset(void)
> > {
> > - struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> > + struct cpu_hw_events *cpuc = get_cpu_ptr(&cpu_hw_events);
> > int i;
> >
> > if (!x86_pmu.lbr_nr)
> > @@ -335,6 +335,7 @@ void amd_pmu_lbr_reset(void)
> >
> > cpuc->last_task_ctx = NULL;
> > cpuc->last_log_id = 0;
> > + put_cpu_ptr(&cpu_hw_events);
> > wrmsrl(MSR_AMD64_LBR_SELECT, 0);
> > }
>
> Weird, amd_pmu_lbr_reset() is called from these places:
>
> - amd_pmu_lbr_sched_task(): during task sched-in during
> context-switching, this should already have preemption disabled.
>
> - amd_pmu_lbr_add(): this gets indirectly called by amd_pmu::add
> (amd_pmu_add_event()), called by event_sched_in(), which too should have
> preemption disabled.
>
> I clearly must have missed some additional place it gets called in.
Just for completeness, the additional place I missed is
amd_pmu_cpu_reset():
static_call(amd_pmu_branch_reset)();
... and the amd_pmu_branch_reset static call is set up with
amd_pmu_lbr_reset, which is why git grep missed it.
Anyway, amd_pmu_cpu_reset() is very much something that should run
non-preemptable to begin with, so your patch only papers over the real
problem AFAICS.
Thanks,
Ingo
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