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

[Christophe Leroy]

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>

> ---
>   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
>