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

[Athira Rajeev]

> On 17-Jun-2021, at 10:05 PM, Christophe Leroy <christophe.leroy at csgroup.eu> wrote:
> 
> 
> 
> Le 17/06/2021 à 08:36, Athira Rajeev a écrit :
>>> On 16-Jun-2021, at 11:56 AM, Christophe Leroy <christophe.leroy at csgroup.eu> 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>
>> Hi Christophe,
>> Thanks for testing with the change. I have a newer version where I have added braces around the check.
>> Can you please check once and can I add your tested-by for the below patch.
> 
> Yes it works, you can add my Tested-by:
> Please also add Cc: stable at vger.kernel.org, this needs to be backported as soon as possible.

Sure Christophe, will add Cc also. Thanks for testing.

Athira
> 
> Thanks
> Christophe