Messages in this thread | | | Subject | Re: [PATCH] perf: fix panic by disable ftrace on fault.c | From | 王贇 <> | Date | Tue, 14 Sep 2021 10:08:45 +0800 |
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On 2021/9/13 下午10:49, Dave Hansen wrote: > On 9/12/21 8:30 PM, 王贇 wrote: >> 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 disable ftrace on fault.c, which help to avoid the panic. > ... >> +# Disable ftrace to avoid stack overflow. >> +CFLAGS_REMOVE_fault.o = $(CC_FLAGS_FTRACE) > > Was this observed on a mainline kernel?
Yes, it is trigger on linux-next.
> > How reproducible is this? > > I suspect we're going into do_user_addr_fault(), then falling in here: > >> if (unlikely(faulthandler_disabled() || !mm)) { >> bad_area_nosemaphore(regs, error_code, address); >> return; >> } >
Correct, perf_callchain_user() disabled PF which lead into here.
> Then something double faults in perf_swevent_get_recursion_context(). > But, you snipped all of the register dump out so I can't quite see > what's going on and what might have caused *that* fault. But, in my > kernel perf_swevent_get_recursion_context+0x0/0x70 is: > > mov $0x27d00,%rdx > > which is rather unlikely to fault.
Would you like to check the full trace I just sent see if we can get any clue?
> > Either way, we don't want to keep ftrace out of fault.c. This patch is > just a hack, and doesn't really try to fix the underlying problem. This > situation *should* be handled today. There's code there to handle it. > > Something else really funky is going on.
Do you think stack overflow is possible in this case? To be mentioned the NMI arrive in very high frequency, and reduce perf_event_max_sample_rate to a low value can also avoid the panic.
Regards, Michael Wang
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