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This is an automatically generated e-mail. To reply, visit:
<a href="https://reviewboard.asterisk.org/r/1100/">https://reviewboard.asterisk.org/r/1100/</a>
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<div>Review request for Asterisk Developers.</div>
<div>By David Vossel.</div>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
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<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">In chan_sip's handle_request_do() function we have to lock both the pvt and the channel at the same time. This involves deadlock avoidance and is a mess. After a number of locking attempts fail on the channel, the request is queued to be handled at a later time. This would typically only occur under very heavy load.
Queued requests are also handled in the handle_request_do() function. Once both a pvt and a channel are locked, the queued requests are handled first, and then the actual request triggering the handle_request_do function's invocation is processed... This is where the problem is.
Between process_request_queue() and calling handle_incoming() the channel may be unlocked. We can detect this by inspecting the nounlock variable which is passed to process_request_queue() but we do not. If the channel remains unlocked entering handle_incoming(), it is very possible a deadlock will occur since many of the code paths in handle_incoming will try to grab a recursive channel lock using the channel API.
This patch detects when the channel has been unlocked during handle_request_do() and attempts to grab the lock again before processing more requests for that dialog.</pre>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
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<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Load tested with 30+ calls a second, verified deadlock does not occur with patch.</pre>
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<b style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Bugs: </b>
<a href="https://issues.asterisk.org/view.php?id=18690">18690</a>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
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<li>trunk/channels/chan_sip.c <span style="color: grey">(307433)</span></li>
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<p><a href="https://reviewboard.asterisk.org/r/1100/diff/" style="margin-left: 3em;">View Diff</a></p>
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