Hitting crash with: event_del_nolock_: noting a del on a non-setup event #1283
Description
Hello,
Some background:
I have wrapped my libevent-2.1.8-stable based C code to use with Python, and I use this with the python-libevent module.
I have used it with many older versions of python, never had a problem. Now, when I tried porting to Python3.8
I hit a crash at event_add() (the event_base is created and maintained from python-libevent and my module does create
and add events).
From valgrind, I could see that there were some memory/ownership issues, so I made both
my module and python-libevent use python's memory allocators (thread-safe) with event_set_mem_functions.
After that, the event_add() works ; but on a timer-event dispatch, I see the crash at event_del_nolock_ !
[debug] event_add: event: 0x13ef960 (fd 6), EV_READ call 0x7fd60de5a707
[debug] Epoll ADD(1) on fd 6 okay. Old events were 0; read change was 1 (add); write change was 0 (none); close change was 0 (none)
[debug] event_add: event: 0x1487ea0 (fd -1), EV_TIMEOUT call 0x7fd60d5a96f6
[debug] event_add: event 0x1487ea0, timeout in 2 seconds 0 useconds, call 0x7fd60d5a96f6
[debug] timeout_next: event: 0x1487ea0, in 2 seconds, 0 useconds
[debug] epoll_dispatch: epoll_wait reports 0
[debug] timeout_next: event: 0x1487ea0, in 0 seconds, 135 useconds
[debug] epoll_dispatch: epoll_wait reports 0
[debug] event_del: 0x1487ea0 (fd -1), callback 0x7fd60d5a96f6
[err] event_del_nolock_: noting a del on a non-setup event 0x1487ea0 (events: 0x0, fd: -1, flags: 0x80)
Aborted (core dumped)
I have enabled pthreads and set the memory functions at the start of both modules (as explained in the documentation).
i.e., both the modules have, at start:
event_set_mem_functions(PyMem_RawMalloc, PyMem_RawRealloc, PyMem_RawFree);
evthread_use_pthreads();
evthread_enable_lock_debugging();
event_enable_debug_mode();
event_enable_debug_logging(EVENT_DBG_ALL);
When run with helgrind, I see :
==2331== Process terminating with default action of signal 6 (SIGABRT): dumping core
==2331== at 0x5C95E87: raise (raise.c:51)
==2331== by 0x5C977F0: abort (abort.c:79)
==2331== by 0x6882389: event_exit (log.c:105)
==2331== by 0x68827D8: event_errx (log.c:162)
==2331== by 0x68758DE: event_del_nolock_ (event.c:2845)
==2331== by 0x68766FD: timeout_process (event.c:3147)
==2331== by 0x6872520: event_base_loop (event.c:1960)
==2331== by 0x685A35D: pybase_loop (pybase.c:159)
...
==2331== Thread #1: Exiting thread still holds 2 locks
Locks at exit should not be a concern (?)
This is not giving much clues! I am not sure if I have to chase memory or locks or threads here ! :-/
Any help, pointers to debug further, much appreciated.
Thanks