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List: asterisk-dev
Subject: Re: [asterisk-dev] [Code Review] Fix broken redirect out of
From: "Russell Bryant" <reviewboard () asterisk ! org>
Date: 2011-01-24 20:17:08
Message-ID: 20110124201708.2750.75572 () hotblack ! digium ! com
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> On 2011-01-24 13:34:48, rmudgett wrote:
> > I don't see anything more to really comment about.
Thanks for the review!
> On 2011-01-24 13:34:48, rmudgett wrote:
> > /branches/1.8/main/features.c, line 734
> > <https://reviewboard.asterisk.org/r/1082/diff/3/?file=15278#file15278line734>
> >
> > I don't know why this line was even here to begin with. I don't think that \
> > _softhangup will ever be nonzero here.
Well, I think I'd like to leave it, and here's why:
1) If it's not needed, it's harmless (just a little bit of extra work in the middle \
of an already expensive operation (transfer)).
2) It is needed for some reason we can't think of, so instead of breaking it to find \
that out, we just leave it and let it keep working. :-)
- Russell
-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://reviewboard.asterisk.org/r/1082/#review3125
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On 2011-01-24 13:07:03, Russell Bryant wrote:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/1082/
> -----------------------------------------------------------
>
> (Updated 2011-01-24 13:07:03)
>
>
> Review request for Asterisk Developers.
>
>
> Summary
> -------
>
> Mantis issue #18585 reports that a channel redirect out of MeetMe() stopped working \
> properly. This issue includes a patch that resolves the issue by removing a call \
> to ast_check_hangup() from app_meetme.c. I left that in my patch, as it doesn't \
> need to be there. However, the rest of the patch fixes this problem with or \
> without the change to app_meetme.
> The key difference between what happens before and after this patch is the effect \
> of the END_OF_Q control frame. After END_OF_Q is hit in ast_read(), ast_read() \
> will return NULL. With the ast_check_hangup() removed, app_meetme sees this which \
> causes it to exit as intended. Checking ast_check_hangup() caused app_meetme to \
> exit earlier in the process, and the target of the redirect saw the condition where \
> ast_read() returned NULL.
> Removing ast_check_hangup() works around the issue in app_meetme, but doesn't solve \
> the issue if another application did the same thing. There are also other edge \
> cases where if an application finishes at the same time that a redirect happens, \
> the target of the redirect will think that the channel hung up. So, I made some \
> changes in pbx.c to resolve it at a deeper level. There are already places that \
> unset the SOFTHANGUP_ASYNCGOTO flag in an attempt to abort the hangup process. My \
> patch extends this to remove the END_OF_Q frame from the channel's read queue, \
> making the "abort hangup" more complete.
>
> This addresses bug 18585.
> https://issues.asterisk.org/view.php?id=18585
>
>
> Diffs
> -----
>
> /branches/1.8/apps/app_meetme.c 303508
> /branches/1.8/include/asterisk/channel.h 303508
> /branches/1.8/main/channel.c 303508
> /branches/1.8/main/features.c 303508
> /branches/1.8/main/pbx.c 303508
>
> Diff: https://reviewboard.asterisk.org/r/1082/diff
>
>
> Testing
> -------
>
> I replicated the bug easily. I verified that removing ast_check_hangup() fixes the \
> issue and determined why it fixes it. I also verified that the issue is resolved \
> with the pbx.c changes, both with and without ast_check_hangup() still used in \
> app_meetme.
>
> Thanks,
>
> Russell
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="https://reviewboard.asterisk.org/r/1082/">https://reviewboard.asterisk.org/r/1082/</a>
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<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <p style="margin-top: 0;">On January 24th, 2011, 1:34 p.m., <b>rmudgett</b> \
wrote:</p> <blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; \
padding-left: 10px;"> <pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; \
white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">I don't \
see anything more to really comment about.</pre> </blockquote>
</blockquote>
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Thanks for the \
review!</pre> <br />
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <p style="margin-top: 0;">On January 24th, 2011, 1:34 p.m., <b>rmudgett</b> \
wrote:</p> <blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; \
padding-left: 10px;">
<table width="100%" border="0" bgcolor="white" style="border: 1px solid #C0C0C0; \
border-collapse: collapse; margin: 2px padding: 2px;"> <thead>
<tr>
<th colspan="4" bgcolor="#F0F0F0" style="border-bottom: 1px solid #C0C0C0; \
font-size: 9pt; padding: 4px 8px; text-align: left;"> <a \
href="https://reviewboard.asterisk.org/r/1082/diff/3/?file=15278#file15278line734" \
style="color: black; font-weight: bold; text-decoration: \
underline;">/branches/1.8/main/features.c</a> <span style="font-weight: normal;">
(Diff revision 3)
</span>
</th>
</tr>
</thead>
<tbody style="background-color: #e4d9cb; padding: 4px 8px; text-align: center;">
<tr>
<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">static \
void check_goto_on_transfer(struct ast_channel *chan)</pre></td>
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</tbody>
<tbody>
<tr>
<th bgcolor="#e9eaa8" style="border-right: 1px solid #C0C0C0;" \
align="right"><font size="2">734</font></th> <td bgcolor="#fdfebc" width="50%"><pre \
style="font-size: 8pt; line-height: 140%; margin: 0; "> xferchan->_softhangup = \
0;</pre></td> <th bgcolor="#e9eaa8" style="border-left: 1px solid #C0C0C0; \
border-right: 1px solid #C0C0C0;" align="right"><font size="2">734</font></th> <td \
bgcolor="#fdfebc" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: \
0; "> ast_channel_clear_softhangup(xferchan, AST_SOFTHANGUP_ALL);</pre></td> </tr>
</tbody>
</table>
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">I don't know why \
this line was even here to begin with. I don't think that _softhangup will ever \
be nonzero here.</pre> </blockquote>
</blockquote>
<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;">Well, I \
think I'd like to leave it, and here's why:
1) If it's not needed, it's harmless (just a little bit of extra work in the \
middle of an already expensive operation (transfer)).
2) It is needed for some reason we can't think of, so instead of breaking it to \
find that out, we just leave it and let it keep working. :-)</pre> <br />
<p>- Russell</p>
<br />
<p>On January 24th, 2011, 1:07 p.m., Russell Bryant wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="8" \
style="background-image: \
url('https://reviewboard.asterisk.orgrb/images/review_request_box_top_bg.png'); \
background-position: left top; background-repeat: repeat-x; border: 1px black \
solid;"> <tr>
<td>
<div>Review request for Asterisk Developers.</div>
<div>By Russell Bryant.</div>
<p style="color: grey;"><i>Updated 2011-01-24 13:07:03</i></p>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0"> <tr>
<td>
<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;">Mantis issue #18585 reports that a channel redirect out of MeetMe() \
stopped working properly. This issue includes a patch that resolves the issue by \
removing a call to ast_check_hangup() from app_meetme.c. I left that in my patch, as \
it doesn't need to be there. However, the rest of the patch fixes this problem \
with or without the change to app_meetme.
The key difference between what happens before and after this patch is the effect of \
the END_OF_Q control frame. After END_OF_Q is hit in ast_read(), ast_read() will \
return NULL. With the ast_check_hangup() removed, app_meetme sees this which causes \
it to exit as intended. Checking ast_check_hangup() caused app_meetme to exit \
earlier in the process, and the target of the redirect saw the condition where \
ast_read() returned NULL.
Removing ast_check_hangup() works around the issue in app_meetme, but doesn't \
solve the issue if another application did the same thing. There are also other edge \
cases where if an application finishes at the same time that a redirect happens, the \
target of the redirect will think that the channel hung up. So, I made some changes \
in pbx.c to resolve it at a deeper level. There are already places that unset the \
SOFTHANGUP_ASYNCGOTO flag in an attempt to abort the hangup process. My patch \
extends this to remove the END_OF_Q frame from the channel's read queue, making \
the "abort hangup" more complete. </pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0"> <tr>
<td>
<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;">I replicated the bug easily. I verified that removing \
ast_check_hangup() fixes the issue and determined why it fixes it. I also verified \
that the issue is resolved with the pbx.c changes, both with and without \
ast_check_hangup() still used in app_meetme.</pre> </td>
</tr>
</table>
<div style="margin-top: 1.5em;">
<b style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Bugs: </b>
<a href="https://issues.asterisk.org/view.php?id=18585">18585</a>
</div>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">
<li>/branches/1.8/apps/app_meetme.c <span style="color: grey">(303508)</span></li>
<li>/branches/1.8/include/asterisk/channel.h <span style="color: \
grey">(303508)</span></li>
<li>/branches/1.8/main/channel.c <span style="color: grey">(303508)</span></li>
<li>/branches/1.8/main/features.c <span style="color: grey">(303508)</span></li>
<li>/branches/1.8/main/pbx.c <span style="color: grey">(303508)</span></li>
</ul>
<p><a href="https://reviewboard.asterisk.org/r/1082/diff/" style="margin-left: \
3em;">View Diff</a></p>
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