[asterisk-bugs] [Asterisk 0018310]: [patch] hint state changes deadlock/race

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=18310 
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Reported By:                one47
Assigned To:                
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Project:                    Asterisk
Issue ID:                   18310
Category:                   Core/PBX
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     ready for testing
Asterisk Version:           1.6.2.14 
JIRA:                       SWP-2541 
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:             2010-11-15 12:19 CST
Last Modified:              2011-01-05 11:11 CST
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Summary:                    [patch] hint state changes deadlock/race
Description: 
VERY similar to https://issues.asterisk.org/view.php?id=18165, but this is a
different deadlock path, so I have
raised a separate report.

Thread 1: taskprocessor  -> handle_statechange
    Lock order = conlock, hints, hint, pvt
Thread 2: chan_sip.c:  handle_request_do -> handle_response_notify
    Lock order = pvt, conlock

Thread2 only gets into the conlock if STATECHANGEQUEUE is true, ie. there
are rapid state changes happening on a subscribed hint.
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Relationships       ID      Summary
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related to          0018165 [patch] hint state changes deadlock pro...
has duplicate       0018535 app_queue deadlocks if weight is set
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 (0130214) one47 (reporter) - 2011-01-05 11:11
 https://issues.asterisk.org/view.php?id=18310#c130214 
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This might be a bit simplistic, but can someone check I am not being
utterly stupid:

At present, I believe that the context-lock is being used to protect the
'statecbs' list. 'statecbs' is managed in main/pbx.c, and is not referenced
anywhere else. Everywhere in main/pbx.c that 'statecbs' is referenced, the
hints-lock is held.

Is the hints lock therefore not sufficient to protect 'statecbs' so that
the context-lock is only held when the context-lock is specifically
needed???

I believe that the possible exception to this is where the dialplan is
being reloaded, and hints potentially created or destroyed. This will be
done from a thread that holds the context-lock while trying to grab and
release the hints lock; I cannot see that being a problem, but could be
wrong...

Thoughts please? 

Issue History 
Date Modified    Username       Field                    Change               
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2011-01-05 11:11 one47          Note Added: 0130214                          
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