[asterisk-dev] [Code Review] Deadlock due to lock order inversion in ast_async_goto()

[kkm]

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Review request for Asterisk Developers and David Vossel.


Summary
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ast_async_goto() grabs a channel lock, and then calls ast_channel_alloc(), which in turn locks the channels container to insert the newly allocated channel into it. That causes nasty deadlocks on servers under load.

I moved the locking of the channel down to after a masquerade channel is allocated.

I do not know how safe it is to assume that the value of (!chan->pbx) won't change while in ast_channel_alloc(). Is a more complex synchronization required here?


This addresses bug ASTERISK-18031.
    https://issues.asterisk.org/jira/browse/ASTERISK-18031


Diffs
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Diff: https://reviewboard.asterisk.org/r/1274/diff


Testing
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Deployed the fix on production servers suffering from deadlocks. They did neither melt nor explode from it, but whether the problem is fixed, I do not know yet. Need to monitor for 2-3 days to be sure.


Thanks,

kkm

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