[asterisk-dev] Interlocking of individual channels and the channels list in chan_sip.
kkm at adaptiveai.com
Thu Jun 16 02:41:33 CDT 2011
I got a deadlock, and do not understand how it can be prevented. Either
that's deep in the design, or I am misunderstanding the rules of
function calling that are violated.
The do_monitor thread gets a REFER on a channel X, then in
handle_refer() gets its bridged channels locked, and calls
ast_async_goto() on that channel. The latter creates a new channel,
attempts to lock the channels list to insert the newly created one, and
Because another thread is in do_devstate_changes(), calls
ast_channel_get_by_name_prefix(), which goes into __ao2_find(channels,
...), that locks the channels list, then invokes ast_channel_cmp_cb() on
every channel (including the channel X) and locks it. It deadlocks on an
attempt to lock the channel. Now the 2 threads are in a first class
I have not filed a bug yet, working on that. But I do not understand how
this type of a deadlock is generally prevented. Since find_channel_...
can be randomly called, the rule should be to never cause an attempted
locking of the channels list while holding a lock on any channel. Correct?
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