[asterisk-bugs] [JIRA] (ASTERISK-24983) IAX deadlock between hangup and scheduled actions (ex. largrq)

[Y Ateya (JIRA)]

Y Ateya created ASTERISK-24983:
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             Summary: IAX deadlock between hangup and scheduled actions (ex. largrq)
                 Key: ASTERISK-24983
                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-24983
             Project: Asterisk
          Issue Type: Bug
      Security Level: None
          Components: Channels/chan_iax2
    Affects Versions: 13.3.2
         Environment: Ubuntu
            Reporter: Y Ateya


Randomly some of my asterisk servers (SIP-to-IAX) _freezes_. After some investigation I found that this happens because of a deadlock between {{iax2_hangup}} and {{send_lagrq}} (It can happen with {{send_ping}} too).

Here is the sequence of _unfortunate_ events to have this deadlock:
  - When a call starts, {{send_lagrq}} is scheduled to run after some time.
  - {{iax2_hangup}} is called.
  - It locks the call number lock {{ast_mutex_lock(&iaxsl\[callno\])}}. Note that later in hangup procedures, we will try to delete scheduled {{send_lagrq}}.
  - Before Deleting {{send_lagrq}}, context switch happened and scheduler found that it is time to run the scheduled {{send_lagrq}}!
  - {{send_lagrq}} is called and tries to acquire call number lock {{ast_mutex_lock(&iaxsl\[callno\])}}. So {{send_lagrq}} is waiting for hangup to finish.
  - After sometime, {{iax2_hangup}} reaches the place to delete scheduled lagrq and ping events. This occurs in function {{iax2_destroy_helper}} by calling {{AST_SCHED_DEL_SPINLOCK(sched, pvt->lagid, &iaxsl\[pvt->callno\])}}, which calls {{ast_sched_del}}, which finds that {{send_lagrq}} is still being serverd {{else if (con->currently_executing && (id == con->currently_executing->id))}}, so it **wait idefinitly**.
  - *Scheduler is blocked*: All events in the scheduler are waiting for this event to finish.
  - *IAX call is blocked*: every one tries to lock the call lock is locked too. After minutes I ended up with hundreds of locked threads.

  
  



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