Summary:ASTERISK-00589: Deadlock, presumable because of ast_debug()
Reporter:cdegroot (cdegroot)Labels:
Date Opened:2003-11-27 16:47:52.000-0600Date Closed:2004-09-25 02:55:01
Versions:Frequency of
Environment:Attachments:( 0) ast-thread-dump.txt
( 1) logger_deadlock.patch
Description:(note: this is an interpretation of the attached file. I think it's correct, but I haven't done a lot of C/threads code lately)

When debugging is on, * is in ast_log() and a sigurg comes in,  ast_log() is called again and the system deadlocks on loglock.


Solution suggestions:
1. suppress signals before ast_mutex_lock(&loglock) and enable again after it;
2. (better, probably) set a static flag when inside ast_log and just return when it's set:

if (inside_log) return;
inside_log = 1;
inside_log = 0;
Comments:By: Mark Spencer (markster) 2003-11-30 17:51:26.000-0600

Dead on.  It never occured to me how we could ever deadlock inside ast_log.  Is it a sufficient workaround to never ast_log inside a signal handler?

By: cdegroot (cdegroot) 2003-12-01 01:47:11.000-0600

Well, I'd rather see ast_log protect itself against a deadlock, at least in that way you have "deadlock insurance" in a single place of the code. But if you can be sure that you cover all the places - for now and in the future - where ast_log() is called inside a signal handler, that should be just fine.

By: Paul Cadach (pcadach) 2003-12-01 04:32:01.000-0600

2Mark: Asterisk gets dead by ast_log() lock when you run it with -d argument and tries to do 'stop now'. 100% reproducible (for me, at least).

Also, I think current realization of inside_log variable manipulation isn't thread-safe and must be "mutexted" too. ;-)'

By: ww (ww) 2003-12-05 14:55:09.000-0600

try the attached patch.
it implements the static variable described
by cdegroot and should fix the deadlock.

really we want a mutex function like

By: ww (ww) 2003-12-05 15:03:22.000-0600

silly me. we do have such a function: ast_mutex_trylock()
and it is thread safe. the logger_deadlock.patch contains
this fix.

By: zoa (zoa) 2004-01-09 21:48:39.000-0600

i just ran asterisk -vvvvvvvvvvvvvvvvvvgcd and did a stop now, didnt see any deadlock so i suppose this got fixed ?

By: zoa (zoa) 2004-01-09 21:48:40.000-0600

i just ran asterisk -vvvvvvvvvvvvvvvvvvgcd and did a stop now, didnt see any deadlock so i suppose this got fixed ?

By: jrollyson (jrollyson) 2004-01-14 03:37:54.000-0600

No longer able to duplicate, presumably fixed in cvs, let me know if you find otherwise.