On 2021/9/13 下午6:24, Peter Zijlstra wrote: > On Mon, Sep 13, 2021 at 11:00:47AM +0800, 王贇 wrote: >> >> >> 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... > > I'm confused tho; where does the #DF come from? Because taking a #PF > from NMI should be perfectly fine. > > AFAICT that callchain is something like: > > NMI > perf_event_nmi_handler() > (part of the chain is missing here) > perf_log_throttle() > perf_output_begin() /* events/ring_buffer.c */ > rcu_read_lock() > rcu_lock_acquire() > lock_acquire() > trace_lock_acquire() --> perf_trace_foo > > ... > perf_callchain() > perf_callchain_user() > #PF (fully expected during a userspace callchain) > (some stuff, until the first __fentry) > perf_trace_function_call > perf_trace_buf_alloc() > perf_swevent_get_recursion_context() > *BOOM* > > Now, supposedly we then take another #PF from get_recursion_context() or > something, but that doesn't make sense. That should just work... > > Can you figure out what's going wrong there? going with the RIP, this > almost looks like 'swhash->recursion' goes splat, but again that makes > no sense, that's a per-cpu variable. That's true, I actually have tried several approach to avoid the issue, but it trigger panic as long as we access 'swhash->recursion', the array should be accessible but somehow broken, that's why I consider this a suspected stack overflow, since nmi repeated and trace seems very long, but just a suspect... Regards, Michael Wang >
