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 10:59, Peter Zijlstra wrote:
> On Tue, Oct 24, 2023 at 10:32:27AM -0500, Mario Limonciello wrote:
>> 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.
> 
> You cut too much; what task is running this?
> 
> 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 #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
  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
  ? srso_alias_return_thunk+0x5/0x7f
  ? count_memcg_events.constprop.0+0x1a/0x30
  ? srso_alias_return_thunk+0x5/0x7f
  ? handle_mm_fault+0x1e9/0x340
  ? srso_alias_return_thunk+0x5/0x7f
  ? preempt_count_add+0x4d/0xa0
  ? srso_alias_return_thunk+0x5/0x7f
  ? up_read+0x38/0x70
  ? srso_alias_return_thunk+0x5/0x7f
  ? do_user_addr_fault+0x343/0x6b0
  ? srso_alias_return_thunk+0x5/0x7f
  ? exc_page_fault+0x74/0x170
  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
RIP: 0033:0x7f32f8d14a77
Code: 10 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e 
fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 
f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
RSP: 002b:00007ffdc648de18 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00007f32f8d14a77
RDX: 0000000000000004 RSI: 000055b2fc2a5670 RDI: 0000000000000004
RBP: 000055b2fc2a5670 R08: 0000000000000000 R09: 000055b2fc2a5670
R10: 00007f32f8e1a2f0 R11: 0000000000000246 R12: 0000000000000004
R13: 000055b2fc2a2480 R14: 00007f32f8e16600 R15: 00007f32f8e15a00
  </TASK>

>>
>> 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
>>