Re: [Libevent-users] deadlock in bufferevent_disable

[Azat Khuzhin <a3at.mail@xxxxxxxxx>]

On Thu, Jan 01, 2015 at 08:46:12AM +0200, Roman Gershman wrote:
> Hi,
> 
> I found the following deadlock bug in libevent code (2.0.21). It looks that
> the problem is in
> bufferevent_disable that locks bufev and transitively calls
> event_del_internal which waits for read callback to finish when it's not in
> the main thread. Meanwhile the main thread calls bufferevent_readcb which
> deadlocks on bufev.
> 
> Is it a known issue? Are there workarounds for this?

Here is the similar issue:
https://github.com/nmathewson/Libevent/issues/105

And also you could read about new feature in 2.1.x: finalizers
http://archives.seul.org/libevent/users/Apr-2013/msg00002.html

I guess this must be fixed with finalizers.
Also if you could post here a ~50L sample I could check it.

> 
> libevent thread:
> 
> #1  0x00007ffff794e672 in _L_lock_953 () from
> /lib/x86_64-linux-gnu/libpthread.so.0
> #2  0x00007ffff794e4da in __GI___pthread_mutex_lock (mutex=0x1031c80) at
> ../nptl/pthread_mutex_lock.c:114
> #3  0x00007ffff771723c in _bufferevent_incref_and_lock
> (bufev=bufev@entry=0x1188c00)
> at bufferevent.c:582
> #4  0x00007ffff771842a in bufferevent_readcb (fd=11, event=<optimized out>,
> arg=0x1188c00) at bufferevent_sock.c:133
> #5  0x00007ffff770df24 in event_process_active_single_queue
> (activeq=0x1024640, base=0x1090000) at event.c:1350
> 
> 
> user thread:
> #0  pthread_cond_wait@@GLIBC_2.3.2 () at
> ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
> #1  0x00007ffff74fdfe5 in evthread_posix_cond_wait (_cond=0x1032430,
> _lock=0x1032460, tv=0x0) at evthread_pthread.c:156
> #2  0x00007ffff770b9ed in event_del_internal (ev=<optimized out>) at
> event.c:2220
> #3  event_del (ev=ev@entry=0x1188c10) at event.c:2188
> #4  0x00007ffff7718645 in be_socket_disable (bufev=0x1188c00,
> event=<optimized out>) at bufferevent_sock.c:570
> #5  0x00007ffff771702b in bufferevent_disable (bufev=0x1188c00,
> event=<optimized out>) at bufferevent.c:505
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