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

From: Peter Zijlstra <[email-masked]>
Date: Fri, 10 Sep 2021 17:38:39 +0200

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?