[asterisk-dev] [Code Review] Fix deadlock between subscription event RWLOCK and dialogs container lock in chan_sip.

[David Vossel]

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Ship it!


- David


On Nov. 8, 2011, 1:42 p.m., rmudgett wrote:
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> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/1557/
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> (Updated Nov. 8, 2011, 1:42 p.m.)
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> 
> Review request for Asterisk Developers, David Vossel and schmidts.
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> Summary
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> Timing between dialog destruction and a MWI event sending a message could result in a deadlock.
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> Order of events causing deadlock:
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> 1a) The event subscription system calls the registered callbacks with its list RWLOCK held.
> 1b) The SIP monitor checks for dialogs needing destruction.  It does an ao2_callback that holds the dialogs container lock while searching for dialogs to destroy.
> 2a) The event subscription SIP callback needs to create a temporary dialog to send out the MWI notification.  That temporary dialog needs to be inserted in the dialogs container so it must wait.
> 2b) The dialog search finds a dialog to destroy and as a result releases the last reference for a peer.  The peer destructor attempts to get the subscription RWLOCK but must wait.
> 3) deadlock
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> 
> Residual changes for Asterisk v10 branch after https://reviewboard.asterisk.org/r/1564/ commit
> and associated dialogs callid hash key change fix.
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> NOTE THE CHANGE FROM v1.8 to v10 BRANCH.
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> * Make check_rtp_timeout() return CMP_MATCH if need to delete dialog from
> dialogs_rtpcheck.  This is an optimization to avoid an unneeded
> lock/unlock and object search when using ao2_unlink.
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> * Prevent crash in check_rtp_timeout() if dialog->rtp is NULL.
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> * Make pvt_set_needdestroy() protect from possible double entries in
> dialogs_needdestroy.
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> Schmidts please note that change_callid_pvt() is different between v1.8
> and v10 for your unleas-the-beast branch.
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> 
> Diffs
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>   /branches/10/channels/chan_sip.c 343951 
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> Diff: https://reviewboard.asterisk.org/r/1557/diff
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> Testing
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> It compiles. :)
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> 
> Thanks,
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> rmudgett
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>

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