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);
> }
>
> /*
>
