[asterisk-bugs] [Asterisk 0018165]: [patch] hint state changes deadlock problem

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=18165 
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Reported By:                antonio
Assigned To:                jpeeler
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Project:                    Asterisk
Issue ID:                   18165
Category:                   Core/PBX
Reproducibility:            have not tried
Severity:                   major
Priority:                   normal
Status:                     assigned
Asterisk Version:           1.6.2.13 
JIRA:                       SWP-2495 
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:             2010-10-19 13:45 CDT
Last Modified:              2010-11-09 11:38 CST
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Summary:                    [patch] hint state changes deadlock problem
Description: 
What happens is there are two threads that lock resources in a different
order causing a deadlock.

The threads are:

1. from taskprocessor handle_statechange() is called. This one locks
ast_rdlock_contexts, and then eventually call cb_extensionstate() which
immediately does a sip_pvt_lock()

2. do_monitor calls sipsock_read() which calls handle_request_do() which
calls find_call(), which does a sip_pvt_lock() too. The incoming request is
a subscription, so it calls ast_get_hint(), which calls
ast_hint_extension() which calls ast_rdlock_contexts(). Deadlock.

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Relationships       ID      Summary
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has duplicate       0018205 PBX hangup
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 (0128723) svnbot (reporter) - 2010-11-09 11:38
 https://issues.asterisk.org/view.php?id=18165#c128723 
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Repository: asterisk
Revision: 294384

U   branches/1.4/include/asterisk.h
U   branches/1.4/main/asterisk.c
U   branches/1.4/main/pbx.c

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r294384 | jpeeler | 2010-11-09 11:38:00 -0600 (Tue, 09 Nov 2010) | 47
lines

Fix a deadlock in device state change processing.

Copied from some notes from the original author (Russell):

Deadlock scenario:
Thread 1: device state change thread
  Holds - rdlock on contexts
  Holds - hints lock
  Waiting on channels container lock

Thread 2: SIP monitor thread
  Holds the "iflock"
  Holds a sip_pvt lock
  Holds channel container lock
  Waiting for a channel lock

Thread 3: A channel thread (chan_local in this case)
  Holds 2 channel locks acquired within app_dial
  Holds a 3rd channel lock it got inside of chan_local
  Holds a local_pvt lock
  Waiting on a rdlock of the contexts lock

A bunch of other threads waiting on a wrlock of the contexts lock


To address this deadlock, some locking order rules must be put in place
and
enforced. Existing relevant rules:

1) channel lock before a pvt lock
2) contexts lock before hints lock
3) channels container before a channel

What's missing is some enforcement of the order when you involve more than
any
two. To fix this problem, I put in some code that ensures that (at least
in the
code paths involved in this bug) the locks in (3) come before the locks in
(2).
To change the operation of thread 1 to comply, I converted the storage of
hints
to an astobj2 container. This allows processing of hints without holding
the
hints container lock. So, in the code path that led to thread 1's state,
it no
longer holds either the contexts or hints lock while it attempts to lock
the
channels container.

(closes issue https://issues.asterisk.org/view.php?id=18165)
Reported by: antonio

ABE-2583


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http://svn.digium.com/view/asterisk?view=rev&revision=294384 

Issue History 
Date Modified    Username       Field                    Change               
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2010-11-09 11:38 svnbot         Note Added: 0128723                          
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