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This is an automatically generated e-mail. To reply, visit:
<a href="https://reviewboard.asterisk.org/r/3548/">https://reviewboard.asterisk.org/r/3548/</a>
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<p style="margin-top: 0;">On June 16th, 2014, 7:04 p.m. UTC, <b>rmudgett</b> wrote:</p>
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<a href="https://reviewboard.asterisk.org/r/3548/diff/2/?file=59691#file59691line1137" style="color: black; font-weight: bold; text-decoration: underline;">/trunk/channels/chan_dahdi.c</a>
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(Diff revision 2)
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span>doomed_list.first = doomed_pris.first;</pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span>doomed_list.last = doomed_pris.last;</pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span>doomed_pris.first = doomed_pris.last = NULL;</pre></td>
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<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">You should not be directly accessing the .first and .last list members directly. This is why I gave you the way it should be done earlier.</pre>
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<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">I explained (and the comment in the code explains) why that does not work: destruction of the spans should not be done with the list lock held - this helps trigger a deadlock, as explained in the bug report. I solve this by moving all entries from a global list to a local list. That way, the lock global list's lock is not held on destruction and the local list doesn't need locking.
linkedlist.h does not have AST_LIST_MOVE (I can add one). Alternatively, I can walk the list and move every single entry. But that just makes the code uglier and does more work under the lock.</pre>
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<p>- Tzafrir</p>
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<p>On June 16th, 2014, 4:07 p.m. UTC, Tzafrir Cohen wrote:</p>
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<div>Review request for Asterisk Developers and rmudgett.</div>
<div>By Tzafrir Cohen.</div>
<p style="color: grey;"><i>Updated June 16, 2014, 4:07 p.m.</i></p>
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<b style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Bugs: </b>
<a href="https://issues.asterisk.org/jira/browse/ASTERISK-23554">ASTERISK-23554</a>
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<b style="color: #575012; font-size: 10pt;">Repository: </b>
Asterisk
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<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;">Issue: when a PRI span is disconnected (e.g.: following the unassignment pri spans) dahdi channels of that span can be destroyed in two different pathes:
1. DAHDI channels are destroyed in response to pri_event_removed
2. The span is destroyed in response to DAHDI_EVENT_REMOVED in the D-channel. Before the span is destroyed, its channels need to be destroyed.
If the channel is not in a call, (1) is run from the monitor thread, holding the iflock (lock of iflist: the list of channels). somewhere in the process of destroying a channel that belongs to a PRI
span, the pri's lock needs to be acquired.
(2) is called from a context of handling the PRI events and hence holds the PRI lock. Destroying the channels requires getting the iflock.
Which means that if the two happen simultaneously, we have a deadlock. And the two will happen simultaneously, as recent versions of DAHDI will send an extra DAHDI_EVENT_REMOVED as a response to any call to the ioctl on DAHDI_GET_EVENT on a removed span.
This review includes the patches pri_destroy_span_prilist.patch and sigpri_handle_enodev_1.patch from the referred bug. The former solves this deadlock by creating a list of spans to be removed "later" and and thus allow executing (2) without holding the pri lock.
The second patch fixes error handling of libpri: if read returns -ENODEV, we have no device and it should be destroyed. This, however, requires exposing the above "deferred destruction" functionality to sig_pri.
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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/sig_pri.c <span style="color: grey">(416393)</span></li>
<li>/trunk/channels/sig_pri.h <span style="color: grey">(416393)</span></li>
<li>/trunk/channels/chan_dahdi.c <span style="color: grey">(416393)</span></li>
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<p><a href="https://reviewboard.asterisk.org/r/3548/diff/" style="margin-left: 3em;">View Diff</a></p>
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