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This is an automatically generated e-mail. To reply, visit:
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<p style="margin-top: 0;">On November 8th, 2011, 11:50 a.m., <b>David Vossel</b> wrote:</p>
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<a href="https://reviewboard.asterisk.org/r/1557/diff/5/?file=21655#file21655line3079" style="color: black; font-weight: bold; text-decoration: underline;">/branches/10/channels/chan_sip.c</a>
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(Diff revision 5)
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<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">static inline void pvt_set_needdestroy(struct sip_pvt *pvt, const char *reason)</pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="p">}</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="p">}</span></pre></td>
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<td bgcolor="#ffc5ce" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="k">if</span><span class="p">(</span><span class="n">pvt</span><span class="o">-></span><span class="n">needdestroy</span> <span class="o">!=</span> <span class="mi">1</span><span class="p">)</span> <span class="p">{</span></pre></td>
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<td bgcolor="#ffc5ce" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_t_link</span><span class="p">(</span><span class="n">dialogs_needdestroy</span><span class="p">,</span> <span class="n">pvt</span><span class="p">,</span> <span class="s">"link pvt into dialogs_needdestroy container"</span><span class="p">);</span></pre></td>
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<td bgcolor="#ffc5ce" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="p">}</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">append_history</span><span class="p">(</span><span class="n">pvt</span><span class="p">,</span> <span class="s">"NeedDestroy"</span><span class="p">,</span> <span class="s">"Setting needdestroy because %s"</span><span class="p">,</span> <span class="n">reason</span><span class="p">);</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">append_history</span><span class="p">(</span><span class="n">pvt</span><span class="p">,</span> <span class="s">"NeedDestroy"</span><span class="p">,</span> <span class="s">"Setting needdestroy because %s"</span><span class="p">,</span> <span class="n">reason</span><span class="p">);</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">pvt</span><span class="o">-></span><span class="n">needdestroy</span><span class="p">)</span> <span class="p">{</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="cm">/*</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> * We unlink this dialog and link again into the</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> * dialogs_needdestroy container so its not in there twice.</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> */</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_lock</span><span class="p">(</span><span class="n">dialogs_needdestroy</span><span class="p">);</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_t_unlink</span><span class="p">(</span><span class="n">dialogs_needdestroy</span><span class="p">,</span> <span class="n">pvt</span><span class="p">,</span> <span class="s">"unlink pvt into dialogs_needdestroy container"</span><span class="p">);</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">pvt</span><span class="o">-></span><span class="n">needdestroy</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">pvt</span><span class="o">-></span><span class="n">needdestroy</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_t_link</span><span class="p">(</span><span class="n">dialogs_needdestroy</span><span class="p">,</span> <span class="n">pvt</span><span class="p">,</span> <span class="s">"link pvt into dialogs_needdestroy container"</span><span class="p">);</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_unlock</span><span class="p">(</span><span class="n">dialogs_needdestroy</span><span class="p">);</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="p">}</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="p">}</span></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;">How would it be possible for something to be linked twice into the needdestroy container? The needdestroy variable should never be set outside of this function, and should definitely never have the potential to be turned off after being set. If this is the case, that is the problem that should be addressed... I see that we do that in sip_hangup. That is wrong. We can never guarantee that setting the pvt->needdestroy variable back to 0 after it is already set will stop anything. That is a nasty race condition that no logic should ever depend on.</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 did the unlink/link because sig_hangup was setting it to zero.</pre>
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<p style="margin-top: 0;">On November 8th, 2011, 11:50 a.m., <b>David Vossel</b> wrote:</p>
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<a href="https://reviewboard.asterisk.org/r/1557/diff/5/?file=21655#file21655line11738" style="color: black; font-weight: bold; text-decoration: underline;">/branches/10/channels/chan_sip.c</a>
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(Diff revision 5)
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<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">static enum sip_result add_sdp(struct sip_request *resp, struct sip_pvt *p, int oldsdp, int add_audio, int add_t38)</pre></td>
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<td bgcolor="#fdfebc" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="cm">/* we unlink this dialog and link again into the dialogs_rtpcheck container to doesnt add it twice */</span></pre></td>
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<td bgcolor="#fdfebc" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="cm">/*</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> * We unlink this dialog and link again into the</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> * dialogs_rtpcheck container so its not in there twice.</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> */</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_lock</span><span class="p">(</span><span class="n">dialogs_rtpcheck</span><span class="p">);</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_t_unlink</span><span class="p">(</span><span class="n">dialogs_rtpcheck</span><span class="p">,</span> <span class="n">p</span><span class="p">,</span> <span class="s">"unlink pvt into dialogs_rtpcheck container"</span><span class="p">);</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_t_unlink</span><span class="p">(</span><span class="n">dialogs_rtpcheck</span><span class="p">,</span> <span class="n">p</span><span class="p">,</span> <span class="s">"unlink pvt into dialogs_rtpcheck container"</span><span class="p">);</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_t_link</span><span class="p">(</span><span class="n">dialogs_rtpcheck</span><span class="p">,</span> <span class="n">p</span><span class="p">,</span> <span class="s">"link pvt into dialogs_rtpcheck container"</span><span class="p">);</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_t_link</span><span class="p">(</span><span class="n">dialogs_rtpcheck</span><span class="p">,</span> <span class="n">p</span><span class="p">,</span> <span class="s">"link pvt into dialogs_rtpcheck container"</span><span class="p">);</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">ao2_unlock</span><span class="p">(</span><span class="n">dialogs_rtpcheck</span><span class="p">);</span></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;">Is p locked during these links/unlinks. If so this is a problem.</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 see what you mean. Deadlock between dialogs_rtpcheck container lock and the dialog p lock. Actually, p is not always locked here which is itself not good.
The dialogs_rtpcheck container does not care about the p lock. The use of the dialogs_rtpcheck container is as a subset of the dialogs container. There are two places where locking order could have been a problem:
1) In dialog_checkrtp_cb() but that function does a trylock instead of a lock.
2) In change_callid_pvt().
Looking at the change_callid_pvt() function will potentially violate locking order between dialogs and dialog/pvt. It is sometimes called with pvt locked. If it is not called with pvt locked then it is changing the dialog callid without the lock. The change_callid_pvt() routine was created from repeated code sequences so it would not be a new deadlock potential.
Locking in chan_sip seems to be really messy. :)</pre>
<br />
<p>- rmudgett</p>
<br />
<p>On November 8th, 2011, 11:19 a.m., rmudgett wrote:</p>
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<div>Review request for Asterisk Developers, David Vossel and schmidts.</div>
<div>By rmudgett.</div>
<p style="color: grey;"><i>Updated Nov. 8, 2011, 11:19 a.m.</i></p>
<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;">Timing between dialog destruction and a MWI event sending a message could result in a deadlock.
Order of events causing deadlock:
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
Residual changes for Asterisk v10 branch after https://reviewboard.asterisk.org/r/1564/ commit
and associated dialogs callid hash key change fix.
NOTE THE CHANGE FROM v1.8 to v10 BRANCH.
* 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.
* Prevent crash in check_rtp_timeout() if dialog->rtp is NULL.
* Make pvt_set_needdestroy() protect from possible double entries in
dialogs_needdestroy.
Schmidts please note that change_callid_pvt() is different between v1.8
and v10 for your unleas-the-beast branch.
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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;">It compiles. :)</pre>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
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<li>/branches/10/channels/chan_sip.c <span style="color: grey">(343850)</span></li>
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<p><a href="https://reviewboard.asterisk.org/r/1557/diff/" style="margin-left: 3em;">View Diff</a></p>
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