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.
