[ClusterLabs] corosync dead loop in segfault handler

[Christine Caulfield]

On 15/02/17 14:50, Jan Friesse wrote:
>> Hi all,
>>
>> Corosync Cluster Engine, version '2.3.4'
>> Copyright (c) 2006-2009 Red Hat, Inc.
>>
>> Today I found corosync consuming 100% cpu. Strace showed following:
>>
>> write(7, "\v\0\0\0", 4)                 = -1 EAGAIN (Resource
>> temporarily unavailable)
>> write(7, "\v\0\0\0", 4)                 = -1 EAGAIN (Resource
>> temporarily unavailable)
>>
>> Then I used gcore to get the coredump.
>>
>> (gdb) bt
>> #0  0x00007f038b74b1cd in write () from /lib64/libpthread.so.0
>> #1  0x00007f038b9656ed in _handle_real_signal_ (signal_num=<optimized
>> out>, si=<optimized out>, context=<optimized out>) at loop_poll.c:474
>> #2  <signal handler called>
>> #3  0x0000000000000000 in ?? ()
>> #4  0x00007f038c220a3d in schedwrk_processor (context=<optimized out>)
>> at sync.c:551
>> #5  0x00007f038c23042b in schedwrk_do (type=<optimized out>,
>> context=0x6a12d56300000001) at schedwrk.c:77
>> #6  0x00007f038bdd49f7 in token_callbacks_execute
>> (type=TOTEM_CALLBACK_TOKEN_SENT, instance=<optimized out>) at
>> totemsrp.c:3493
>> #7  message_handler_orf_token (instance=<optimized out>,
>> msg=<optimized out>, endian_conversion_needed=<optimized out>,
>> msg_len=<optimized out>) at totemsrp.c:3894
>> #8  0x00007f038bdd65a5 in message_handler_orf_token
>> (instance=<optimized out>, msg=<optimized out>, msg_len=<optimized
>> out>, endian_conversion_needed=<optimized out>) at totemsrp.c:3609
>> #9  0x00007f038bdcdfb9 in rrp_deliver_fn (context=0x7f038d541840,
>> msg=0x7f038d541af8, msg_len=70) at totemrrp.c:1941
>> #10 0x00007f038bdca01e in net_deliver_fn (fd=<optimized out>,
>> revents=<optimized out>, data=0x7f038d541a90) at totemudpu.c:499
>> #11 0x00007f038b96576f in _poll_dispatch_and_take_back_
>> (item=0x7f038d4fe168, p=<optimized out>) at loop_poll.c:108
>> #12 0x00007f038b965300 in qb_loop_run_level (level=0x7f038d4fde08) at
>> loop.c:43
>> #13 qb_loop_run (lp=<optimized out>) at loop.c:210
>> #14 0x00007f038c21b6d0 in main (argc=<optimized out>, argv=<optimized
>> out>, envp=<optimized out>) at main.c:1383
>>
>> (gdb) f 1
>> #1  0x00007f038b9656ed in _handle_real_signal_ (signal_num=<optimized
>> out>, si=<optimized out>, context=<optimized out>) at loop_poll.c:474
>> 474                     res = write(pipe_fds[1], &sig, sizeof(int32_t));
>> (gdb) info locals
>> sig = 11
>> res = <optimized out>
>> __func__ = "_handle_real_signal_"
>> (gdb) f 4
>> #4  0x00007f038c220a3d in schedwrk_processor (context=<optimized out>)
>> at sync.c:551
>> 551                            
>> my_service_list[my_processing_idx].sync_init (my_trans_list,
>> (gdb) p my_processing_idx
>> $31 = 3
>> (gdb) p my_service_list[3]
>> $32 = {service_id = 0, sync_init = 0x0, sync_abort = 0x0, sync_process
>> = 0x0, sync_activate = 0x0, state = PROCESS, name = '\000 <repeats 127
>> times>}
>>
>> So it seems  corosync dead looping in segfault handler.
>> I have not found any related changelog in the release notes after 2.3.4.
>>
>> Can anyone help please?
> 
> Yep. It looks like (for some reason) signal pipe was not processed and
> libqb _handle_real_signal_ is looping. Corosync really cannot do
> anything about it. It looks like regular libqb bug, so even you can't do
> anything with it. CCing Chrissie so she is aware.
> 

Yes, it seems that some corosync SEGVs trigger this obscure bug in
libqb. I've chased a few possible causes and none have been fruitful.

If you get this then corosync has crashed, and this other bug is masking
the actual diagnostics - I know, helpful :/

It's on my list

Chrissie