Re: [PATCH 2/2] perf/x86/amd: Don't allow pre-emption in amd_pmu_lbr_reset()

[Mario Limonciello]

On 10/24/2023 03:02, Ingo Molnar wrote:
> * Mario Limonciello <mario.limonciello@xxxxxxx> 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@xxxxxxxxxxxxxxx # 6.1+
> > Fixes: ca5b7c0d9621 ("perf/x86/amd/lbr: Add LbrExtV2 branch record support")
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> >   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.
>
> Could you please cite the full log of the amd_pmu_lbr_reset() call that
> caused the critical section warning?
>
> Thanks,
>
> 	Ingo

Below is the call trace in case you think it's better to disable 
preemption by the caller instead.  If you think it's better to keep it 
in amd_pmu_lbr_reset() I'll add this trace to the commit message.

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
 suspend_devices_and_enter+0x342/0x900
 pm_suspend+0x2fd/0x690
 state_store+0x71/0xd0
 kernfs_fop_write_iter+0x128/0x1c0
 vfs_write+0x2db/0x400
 ksys_write+0x5f/0xe0
 do_syscall_64+0x59/0x90