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

[Mario Limonciello <mario.limonciello@amd.com>]

On 10/24/2023 03:02, Ingo Molnar wrote:
> 
> * Mario Limonciello <mario.limonciello@amd.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@vger.kernel.org # 6.1+
>> Fixes: ca5b7c0d9621 ("perf/x86/amd/lbr: Add LbrExtV2 branch record support")
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.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.
> 
> 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