Date: Sat, 7 Nov 2020 16:12:18 -0800 From: Pete Wright <pete@nomadlogic.org> To: Patrick Mahan <plmahan@gmail.com> Cc: questions list <freebsd-questions@freebsd.org> Subject: Re: Helping understand cause of SIGSEGV Message-ID: <46c6e046-8786-8142-0e4f-7c5ec407b3f4@nomadlogic.org> In-Reply-To: <CAFDHx1JDyJq%2Bsepz1O186AeijTqyXP6AuQajsETY00j5eAsLXQ@mail.gmail.com> References: <c2eab4b0-b10b-9db3-1aa3-1f61689e24e8@nomadlogic.org> <CAFDHx1Jg_9k3oWU8X-WdP2CJX8hnBYgMz%2BvxwOs766JZcM3WRQ@mail.gmail.com> <0764e7ef-bd81-a6c5-47c4-7cd539a428f5@nomadlogic.org> <CAFDHx1K2-RWS4=xYtNUKMV3t_J7OKKPUE56f9JY45Q%2B0nH_TFA@mail.gmail.com> <f51dfaf6-46da-9cd8-ea37-b2733f5ad9bc@nomadlogic.org> <CAFDHx1JDyJq%2Bsepz1O186AeijTqyXP6AuQajsETY00j5eAsLXQ@mail.gmail.com>
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On 11/7/20 11:57 AM, Patrick Mahan wrote: > On Sat, Nov 7, 2020 at 9:59 AM Pete Wright <pete@nomadlogic.org> wrote: > >> >> On 11/5/20 9:44 PM, Patrick Mahan wrote: >> >> On Thu, Nov 5, 2020 at 5:01 PM Pete Wright <pete@nomadlogic.org> wrote: >> >>> >>> On 11/5/20 4:01 PM, Patrick Mahan wrote: >>> >>> >>> >>>> | thread #1, name = 'fluent-bit', stop reason = signal SIGABRT >>>> * frame #0: 0x000000004087100a libc.so.7`__sys_thr_kill at >>>> thr_kill.S:4 >>>> frame #1: 0x00000000407e6c84 libc.so.7`__raise(s=6) at raise.c:52:10 >>>> frame #2: 0x000000004089a5d9 libc.so.7`abort at abort.c:67:8 >>>> frame #3: 0x000000000034a7a8 >>>> fluent-bit`flb_signal_handler(signal=11) at fluent-bit.c:418:9 >>>> frame #4: 0x00000000406d1c20 >>>> libthr.so.3`handle_signal(actp=0x00007fffdfffc600, sig=11, >>>> info=0x00007fffdfffc9f0, ucp=0x00007fffdfffc680) at thr_sig.c:303:3 >>>> frame #5: 0x00000000406d11ef libthr.so.3`thr_sighandler(sig=11, >>>> info=0x00007fffdfffc9f0, _ucp=0x00007fffdfffc680) at thr_sig.c:246:2 >>>> frame #6: 0x00007fffffffe193 >>>> frame #7: 0x000000000036fe0c fluent-bit`tasks_start [inlined] >>>> output_params_set(th=0x00000000416091c0, data=0x000000004165d980, >>>> bytes=128, tag="random.0", tag_len=8, i_ins=0x0000000040e58000, >>>> out_plugin=0x0000000040e2dfc0, out_context=0x00000000416051e0, >>>> config=0x0000000040e19180) at flb_output.h:429:5 >>>> >>> I would look at what is happening here in output_params_set(). Something >>> is accessing out of bounds memory. >>> >>> >>> >>> thanks for your response Patrick i really appreciate it. >>> >>> So here is where output_params_set() is defined - with an interesting >>> comment that i haven't chased down yet: >>> >>> 521 /* Workaround for makecontext() */ >>> 522 output_params_set(th, >>> 523 buf, >>> 524 size, >>> 525 tag, >>> 526 tag_len, >>> 527 i_ins, >>> 528 o_ins->p, >>> 529 o_ins->context, >>> 530 config); >>> 531 return th; >>> 532 } >>> 533 >>> >>> and the frame from the backtrace is this for reference: >>> frame #8: 0x000000000036fd14 fluent-bit`tasks_start [inlined] >>> flb_output_thread(task=0x00000000416410a0, i_ins=0x0000000040e58000, >>> o_ins=0x0000000040e5b000, config=0x0000000040e19180, >>> buf=0x000000004165d980, size=128, tag="random.0", tag_len=8) at >>> flb_output.h:522 >>> >>> and then later on line 429 of flb_output.h it does this: >>> 428 FLB_TLS_SET(flb_libco_params, params); >>> 429 co_switch(th->callee); >>> >>> like i said i'm not really sure how to grok this, but it sounds like one >>> of the params in output_params_set isn't being set correctly. hopefully >>> the code snippet makes the error more obvious :) >>> >>> >> Okay, I don't know lldb very well. But according to the GDB to LLDB >> command map <http://lldb.llvm.org/use/map.html>; it uses the same commands >> to move between frames. So at startup you want to ensure you are in thread >> 1 (thread select 1). That should place you in the last frame on the stack >> (frame #0). You just move up the stack using the command 'up' until you >> are in frame #7. >> >> Once there you need to dump the contents of 'th' using the command 'p *th' >> or 'frame variable -T *th'. I suspect the value of th->callee is >> incorrect. The next frame on the stack is - >> >> frame #6: 0x00007fffffffe193 >> >> This is different from the rest of the stack addresses. So I suspect it >> is out of bounds. >> >> Patrick >> >> >> >> that's totally it - thanks Patrick! >> >> frame #7: 0x000000000036fe0c fluent-bit`tasks_start [inlined] >> output_params_set(th=0x00000000416091c0, data=0x000000004165d980, >> bytes=128, tag="random.0", tag_len=8, i_ins=0x0000000040e58000, >> out_plugin=0x0000000040e2dfc0, out_context=0x00000000416051e0, >> config=0x0000000040e19180) at flb_output.h:429:5 >> 426 params->th = th; >> 427 >> 428 FLB_TLS_SET(flb_libco_params, params); >> -> 429 co_switch(th->callee); >> 430 } >> 431 >> 432 static FLB_INLINE void output_pre_cb_flush(void) >> (lldb) p *th >> (flb_thread) $0 = { >> caller = 0x00000000406b2950 >> callee = 0x000000004169f640 >> data = 0xa5a5a5a5a5a5a5a5 >> cb_destroy = 0x0000000000000000 >> } >> (lldb) >> >> i guess the next question to answer is why is this out of bounds. i'm >> gonna poke around and see what i can learn today. >> >> > The value of th->callee should be a function, I think. That is just from a > cursory glance at libco. > > Good luck. interesting - so it looks like fluent-bit includes their own version of libco under lib/flb_libco. i didn't observe any major differences from it's upstream via a cursory glance. the included doc has this to say about co_switch(): void co_switch(cothread_t cothread) Switch to specified cothread. Null (0) or invalid cothread handle is not allowed. Passing handle of active cothread to this function is not allowed. looking through their flb_thread_libco.h file the implementation looks like this: #define flb_thread_return(th) co_switch(th->caller) static FLB_INLINE void flb_thread_resume(struct flb_thread *th) { pthread_setspecific(flb_thread_key, (void *) th); /* * In the past we used to have a flag to mark when a coroutine * has finished (th->ended == MK_TRUE), now we let the coroutine * to submit an event to the event loop indicating what's going on * through the call FLB_OUTPUT_RETURN(...). * * So we just swap context and let the event loop to handle all * the cleanup required. */ th->caller = co_active(); co_switch(th->callee); } the above code is old (from 2016) so i don't think that's the issue. thanks for your help on the Patrick - i suspect to make much more progress i'll need someone from the fluent-bit team to take a closer look as to what's happening. cheers, -pete -- Pete Wright pete@nomadlogic.org @nomadlogicLA
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