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

[王贇]

Reported-by: Abaci <abaci@xxxxxxxxxxxxxxxxx>

On 2021/9/9 上午11:13, 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
> 
> According to the trace we know the story is like this, the NMI
> triggered perf IRQ throttling and call perf_log_throttle(),
> which triggered the swevent overflow, and the overflow process
> do perf_callchain_user() which triggered a user PF, and the PF
> process triggered perf ftrace which finally lead into a suspected
> stack overflow.
> 
> This patch marking the context as recursion during perf_log_throttle()
> , so no more swevent during the process and no more panic.
> 
> Signed-off-by: Michael Wang <yun.wang@xxxxxxxxxxxxxxxxx>
> ---
>  kernel/events/core.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 744e872..6063443 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8716,6 +8716,7 @@ static void perf_log_throttle(struct perf_event *event, int enable)
>  	struct perf_output_handle handle;
>  	struct perf_sample_data sample;
>  	int ret;
> +	int rctx;
> 
>  	struct {
>  		struct perf_event_header	header;
> @@ -8738,14 +8739,17 @@ static void perf_log_throttle(struct perf_event *event, int enable)
> 
>  	perf_event_header__init_id(&throttle_event.header, &sample, event);
> 
> +	rctx = perf_swevent_get_recursion_context();
>  	ret = perf_output_begin(&handle, &sample, event,
>  				throttle_event.header.size);
> -	if (ret)
> -		return;
> +	if (!ret) {
> +		perf_output_put(&handle, throttle_event);
> +		perf_event__output_id_sample(event, &handle, &sample);
> +		perf_output_end(&handle);
> +	}
> 
> -	perf_output_put(&handle, throttle_event);
> -	perf_event__output_id_sample(event, &handle, &sample);
> -	perf_output_end(&handle);
> +	if (rctx >= 0)
> +		perf_swevent_put_recursion_context(rctx);
>  }
> 
>  /*
>