Oops (NULL pointer) with 'perf record' of selftest 'null_syscall'

[Madhavan Srinivasan]

On 6/16/21 11:56 AM, Christophe Leroy wrote:
>
>
> Le 16/06/2021 à 05:40, Athira Rajeev a écrit :
>>
>>
>>> On 16-Jun-2021, at 8:53 AM, Madhavan Srinivasan 
>>> <maddy at linux.ibm.com> wrote:
>>>
>>>
>>> On 6/15/21 8:35 PM, Christophe Leroy wrote:
>>>> For your information, I'm getting the following Oops. Detected with 
>>>> 5.13-rc6, it also oopses on 5.12 and 5.11.
>>>> Runs ok on 5.10. I'm starting bisecting now.
>>>
>>>
>>> Thanks for reporting, got the issue. What has happened in this case 
>>> is that, pmu device is not registered
>>> and trying to access the instruction point which will land in 
>>> perf_instruction_pointer(). And recently I have added
>>> a workaround patch for power10 DD1 which has caused this breakage. 
>>> My bad. We are working on a fix patch
>>> for the same and will post it out. Sorry again.
>>>
>>
>> Hi Christophe,
>>
>> Can you please try with below patch in your environment and test if 
>> it works for you.
>>
>>  From 55d3afc9369dfbe28a7152c8e9f856c11c7fe43d Mon Sep 17 00:00:00 2001
>> From: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
>> Date: Tue, 15 Jun 2021 22:28:11 -0400
>> Subject: [PATCH] powerpc/perf: Fix crash with 
>> 'perf_instruction_pointer' when
>>   pmu is not set
>>
>> On systems without any specific PMU driver support registered, running
>> perf record causes oops:
>>
>> [   38.841073] NIP [c00000000013af54] 
>> perf_instruction_pointer+0x24/0x100
>> [   38.841079] LR [c0000000003c7358] perf_prepare_sample+0x4e8/0x820
>> [   38.841085] --- interrupt: 300
>> [   38.841088] [c00000001cf03440] [c0000000003c6ef8] 
>> perf_prepare_sample+0x88/0x820 (unreliable)
>> [   38.841096] [c00000001cf034a0] [c0000000003c76d0] 
>> perf_event_output_forward+0x40/0xc0
>> [   38.841104] [c00000001cf03520] [c0000000003b45e8] 
>> __perf_event_overflow+0x88/0x1b0
>> [   38.841112] [c00000001cf03570] [c0000000003b480c] 
>> perf_swevent_hrtimer+0xfc/0x1a0
>> [   38.841119] [c00000001cf03740] [c0000000002399cc] 
>> __hrtimer_run_queues+0x17c/0x380
>> [   38.841127] [c00000001cf037c0] [c00000000023a5f8] 
>> hrtimer_interrupt+0x128/0x2f0
>> [   38.841135] [c00000001cf03870] [c00000000002962c] 
>> timer_interrupt+0x13c/0x370
>> [   38.841143i] [c00000001cf038d0] [c000000000009ba4] 
>> decrementer_common_virt+0x1a4/0x1b0
>> [   38.841151] --- interrupt: 900 at copypage_power7+0xd4/0x1c0
>>
>> During perf record session, perf_instruction_pointer() is called to
>> capture the sample ip. This function in core-book3s accesses 
>> ppmu->flags.
>> If a platform specific PMU driver is not registered, ppmu is set to NULL
>> and accessing its members results in a crash. Fix this crash by checking
>> if ppmu is set.
>>
>> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
>> Reported-by: Christophe Leroy <christophe.leroy at csgroup.eu>
>
> Fixes: 2ca13a4cc56c ("powerpc/perf: Use regs->nip when SIAR is zero")
> Cc: stable at vger.kernel.org
> Tested-by: Christophe Leroy <christophe.leroy at csgroup.eu>
Thanks, but just wonder what is the system config and processor version 
in which you got this fail.
Reason, we do have generic-pmu which should kick-in in absence of a 
platform specific driver.

Maddy
>
>> ---
>>   arch/powerpc/perf/core-book3s.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/perf/core-book3s.c 
>> b/arch/powerpc/perf/core-book3s.c
>> index 16d4d1b6a1ff..816756588cb7 100644
>> --- a/arch/powerpc/perf/core-book3s.c
>> +++ b/arch/powerpc/perf/core-book3s.c
>> @@ -2254,7 +2254,7 @@ unsigned long perf_instruction_pointer(struct 
>> pt_regs *regs)
>>       bool use_siar = regs_use_siar(regs);
>>       unsigned long siar = mfspr(SPRN_SIAR);
>>   -    if (ppmu->flags & PPMU_P10_DD1) {
>> +    if (ppmu && ppmu->flags & PPMU_P10_DD1) {
>>           if (siar)
>>               return siar;
>>           else
>>