[asterisk-bugs] [Asterisk 0017407]: [patch] DEADLOCK_AVOIDANCE can actually generate dealocks

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=17407 
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Reported By:                pdf
Assigned To:                
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Project:                    Asterisk
Issue ID:                   17407
Category:                   Core/General
Reproducibility:            sometimes
Severity:                   block
Priority:                   normal
Status:                     ready for testing
Target Version:             1.4.33
Asterisk Version:           1.4.31 
JIRA:                       SWP-1584 
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2010-05-27 00:23 CDT
Last Modified:              2010-05-27 18:40 CDT
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Summary:                    [patch] DEADLOCK_AVOIDANCE can actually generate
dealocks
Description: 
We have reported this issue to Digium support, however were asked to submit
the patch via this tracker.

In brief: the DEADLOCK_AVOIDANCE macro attempts to release an existing
lock, then relock after a usleep(1), to allow other code to proceed around
the lock.  However, it doesn't actually check to see if a lock was released
by the unlock, before taking a new lock.  This means that whenever there is
no lock released, a new lock is taken that will never be released, meaning
that DEADLOCK_AVOIDANCE actually leaks locks, which can obviously lead to a
deadlock.
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 (0122589) pdf (reporter) - 2010-05-27 18:40
 https://issues.asterisk.org/view.php?id=17407#c122589 
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Adding some logging is certainly a good idea, and will help find coding
errors, but leaving the existing code in place means that any time someone
calls DEADLOCK_AVOIDANCE outside a lock, they'll leak a lock and will get
stuck on it later.  Surely it's better to (perhaps log first as you say)
continue if called unnecessarily, rather than potentially bring the whole
box to a halt by adding a lock that will never be released? 

Issue History 
Date Modified    Username       Field                    Change               
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2010-05-27 18:40 pdf            Note Added: 0122589                          
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