[asterisk-dev] [Code Review] Deadlocks dealing with dialplan hints during reload.

[rmudgett]

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https://reviewboard.asterisk.org/r/1313/
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Review request for Asterisk Developers, Russell Bryant and David Vossel.


Summary
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There are two remaining different deadlocks reported dealing with dialplan
hints.

The deadlock in ASTERISK-17666 is caused by invalid locking order in
ast_remove_hint().  The hints container must be locked before the hint
object.

The deadlock in ASTERISK-17760 is caused by a catch-22 situation in
handle_statechange().  The deadlock is caused by not having the conlock
before calling the watcher callbacks.  Unfortunately, having that lock
causes a different deadlock as reported in ASTERISK-16961.

* Fixed ast_remove_hint() locking order.

* Made handle_statechange() no longer call the watcher callbacks holding
any locks that matter.

* Made hint ao2 destructor do the watcher callbacks for extension
deactivation to guarantee that they get called.

* Fixed hint reference leak in ast_add_hint() if the callback container
constructor failed.

* Fixed hint reference leak in complete_core_show_hint() for every hint it
found for CLI tab completion.

* Adjusted locking in ast_merge_contexts_and_delete() for safety.

* Added context_merge_lock to prevent ast_merge_contexts_and_delete() and
handle_statechange() from interfering with each other.


This addresses bugs ASTERISK-17666 and ASTERISK-17760.
    https://issues.asterisk.org/jira/browse/ASTERISK-17666
    https://issues.asterisk.org/jira/browse/ASTERISK-17760


Diffs
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  /branches/1.8/main/pbx.c 327043 

Diff: https://reviewboard.asterisk.org/r/1313/diff


Testing
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* Did some calls that changed the state of some hints.
* Reloaded the dialplan.


Thanks,

rmudgett

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