Re: [RFC PATCH] perf: fix panic by mark recursion inside perf_log_throttle

[王贇]

On 2021/9/10 下午11:38, Peter Zijlstra wrote:
> On Thu, Sep 09, 2021 at 11:13:21AM +0800, 王贇 wrote:
>> When running with ftrace function enabled, we observed panic
>> as below:
>>
>>   traps: PANIC: double fault, error_code: 0x0
>>   [snip]
>>   RIP: 0010:perf_swevent_get_recursion_context+0x0/0x70
>>   [snip]
>>   Call Trace:
>>    <NMI>
>>    perf_trace_buf_alloc+0x26/0xd0
>>    perf_ftrace_function_call+0x18f/0x2e0
>>    kernelmode_fixup_or_oops+0x5/0x120
>>    __bad_area_nosemaphore+0x1b8/0x280
>>    do_user_addr_fault+0x410/0x920
>>    exc_page_fault+0x92/0x300
>>    asm_exc_page_fault+0x1e/0x30
>>   RIP: 0010:__get_user_nocheck_8+0x6/0x13
>>    perf_callchain_user+0x266/0x2f0
>>    get_perf_callchain+0x194/0x210
>>    perf_callchain+0xa3/0xc0
>>    perf_prepare_sample+0xa5/0xa60
>>    perf_event_output_forward+0x7b/0x1b0
>>    __perf_event_overflow+0x67/0x120
>>    perf_swevent_overflow+0xcb/0x110
>>    perf_swevent_event+0xb0/0xf0
>>    perf_tp_event+0x292/0x410
>>    perf_trace_run_bpf_submit+0x87/0xc0
>>    perf_trace_lock_acquire+0x12b/0x170
>>    lock_acquire+0x1bf/0x2e0
>>    perf_output_begin+0x70/0x4b0
>>    perf_log_throttle+0xe2/0x1a0
>>    perf_event_nmi_handler+0x30/0x50
>>    nmi_handle+0xba/0x2a0
>>    default_do_nmi+0x45/0xf0
>>    exc_nmi+0x155/0x170
>>    end_repeat_nmi+0x16/0x55
> 
> kernel/events/Makefile has:
> 
> ifdef CONFIG_FUNCTION_TRACER
> CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
> endif
> 
> Which, afaict, should avoid the above, no?

I'm afraid it's not working for this case, the
start point of tracing is at lock_acquire() which
is not from 'kernel/events/core', the following PF
related function are also not from 'core', prevent
ftrace on 'core' can't prevent this from happen...

Regards,
Michael Wang

>