[asterisk-dev] [Code Review] 2961: Add channel locking for calls that result in channel snapshot creation

Mark Michelson reviewboard at asterisk.org
Tue Nov 19 12:42:20 CST 2013 


> On Nov. 19, 2013, 3:02 a.m., rmudgett wrote:
> >

So, it appears that I applied the incorrect diff to this review, and that is why it seems that some of your comments from before were not addressed.


> On Nov. 19, 2013, 3:02 a.m., rmudgett wrote:
> > /branches/12/channels/chan_pjsip.c, lines 580-587
> > <https://reviewboard.asterisk.org/r/2961/diff/2/?file=48220#file48220line580>
> >
> >     Is it safe to do these finds with the channel locked?

It indeed is not. Good catch. I'll fix it by moving the ao2_finds to before the channel is locked.


> On Nov. 19, 2013, 3:02 a.m., rmudgett wrote:
> > /branches/12/res/res_agi.c, line 3688
> > <https://reviewboard.asterisk.org/r/2961/diff/2/?file=48249#file48249line3688>
> >
> >     Need to lock chan around this call.
> >     
> >     Check if these other places need locking added:
> >     aoc.c:1874
> >     chan_sip.c:28824
> >     channel.c:3629
> >     channel.c:3646
> >     pbx.c:5793
> >     stasis_channels.c:667

I fixed the res_agi.c call.

In all of the other places you've mentioned, the channel is already locked when control reaches the line you pointed out. In the case of ast_aoc_manager_event() and ast_channel_publish_varset(), they have had their documentation altered to indicate the precondition of having the channel locked.


- Mark


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On Nov. 13, 2013, 6:59 p.m., Mark Michelson wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/2961/
> -----------------------------------------------------------
> 
> (Updated Nov. 13, 2013, 6:59 p.m.)
> 
> 
> Review request for Asterisk Developers.
> 
> 
> Bugs: ASTERISK-22709
>     https://issues.asterisk.org/jira/browse/ASTERISK-22709
> 
> 
> Repository: Asterisk
> 
> 
> Description
> -------
> 
> John Bigelow discovered that if the newly-created atxfer_threeway_nominal test is run in a loop, eventually a test run will cause the UUT instance of Asterisk to crash. Investigation of the crash showed that the crash was being caused while trying to get the string representation of a channel's translation paths while creating a channel snapshot. The attended transfer manager thread was creating the channel snapshot as part of the attended transfer stasis message while in another thread (in this case, the bridge channel thread) the translation paths were being altered to make the channel compatible with others in the bridge.
> 
> It's clear that the issue is that the channel's contents are not lock protected while creating a channel snapshot. Luckily, the channel's lock is held already when updating translation paths. By adding locking, I was able to run the test over 450 times straight with no negative consequences.
> 
> When adding locking, there were two strategies to follow:
> 
> 1) Take advantage of the fact that channel locks are recursive, and just add a single SCOPED_CHANNELLOCK() call to ast_channel_snapshot_create() and call it a day.
> 2) Make an audit of channel-related calls that end up creating a channel snapshot and require locks be held prior to making those calls.
> 
> I like approach 2 more, even though it's harder to pull off. In investigating what paths result in channel snapshots being created, I found that channel locks should be required before calling the following functions:
> 
> * ast_channel_snapshot_create()
> * ast_channel_blob_create()
> * ast_channel_publish_snapshot()
> * ast_publish_channel_state()
> * ast_channel_publish_blob()
> * ast_channel_publish_varset()
> * ast_channel_amaflags_set()
> * ast_channel_callid_set()
> * ast_channel_whentohangup_set()
> * ast_channel_callgroup_set()
> * ast_channel_pickupgroup_set()
> * ast_channel_internal_bridge_set()
> * ast_channel_language_set()
> * ast_channel_accountcode_set()
> * ast_channel_peeraccount_set()
> * ast_channel_linkedid_set()
> * ast_channel_stage_snapshot()
> * ast_setstate()
> * ast_aoc_manager_event()
> * ast_channel_setwhentohangup_tv()
> * ast_channel_setwhentohangup()
> * ast_set_variables()
> 
> All of these functions' documentation have been updated to indicate a precondition of having the channel locked.
> 
> In addition, there are some more complex functions that create channel snapshots but could not easily be made to have the precondition of having the channel locked. These are:
> 
> * ast_bridge_blob_create()
> * ast_publish_attended_transfer_fail()
> * ast_publish_attended_transfer_bridge_merge()
> * ast_publish_attended_transfer_threeway()
> * ast_publish_attended_transfer_app()
> * ast_publish_attended_transfer_link()
> * ast_bridge_publish_enter()
> * ast_bridge_publish_leave()
> * ast_bridge_publish_blind_transfer()
> 
> These functions' documentation now have a precondition of having no channels or bridges locked.
> 
> This review seeks only to make sure that channels are properly locked prior to creating channel snapshots. A similar effort is likely needed to ensure that bridges are locked during bridge snapshot creation.
> 
> 
> Diffs
> -----
> 
>   /branches/12/tests/test_stasis_channels.c 402686 
>   /branches/12/tests/test_cel.c 402686 
>   /branches/12/tests/test_cdr.c 402686 
>   /branches/12/res/res_stasis.c 402686 
>   /branches/12/res/res_pjsip_refer.c 402686 
>   /branches/12/res/res_agi.c 402686 
>   /branches/12/res/parking/parking_manager.c 402686 
>   /branches/12/res/parking/parking_bridge_features.c 402686 
>   /branches/12/res/ari/resource_bridges.c 402686 
>   /branches/12/pbx/pbx_realtime.c 402686 
>   /branches/12/main/stasis_channels.c 402686 
>   /branches/12/main/stasis_bridges.c 402686 
>   /branches/12/main/pickup.c 402686 
>   /branches/12/main/pbx.c 402686 
>   /branches/12/main/endpoints.c 402686 
>   /branches/12/main/dial.c 402686 
>   /branches/12/main/core_unreal.c 402686 
>   /branches/12/main/core_local.c 402686 
>   /branches/12/main/channel.c 402769 
>   /branches/12/main/cel.c 402686 
>   /branches/12/main/bridge_channel.c 402686 
>   /branches/12/main/bridge.c 402686 
>   /branches/12/include/asterisk/stasis_channels.h 402686 
>   /branches/12/include/asterisk/stasis_bridges.h 402686 
>   /branches/12/include/asterisk/channelstate.h 402686 
>   /branches/12/include/asterisk/channel.h 402686 
>   /branches/12/include/asterisk/aoc.h 402686 
>   /branches/12/funcs/func_timeout.c 402686 
>   /branches/12/channels/sig_pri.c 402686 
>   /branches/12/channels/sig_analog.c 402686 
>   /branches/12/channels/chan_vpb.cc 402686 
>   /branches/12/channels/chan_unistim.c 402686 
>   /branches/12/channels/chan_skinny.c 402686 
>   /branches/12/channels/chan_sip.c 402686 
>   /branches/12/channels/chan_pjsip.c 402686 
>   /branches/12/channels/chan_phone.c 402686 
>   /branches/12/channels/chan_oss.c 402686 
>   /branches/12/channels/chan_nbs.c 402686 
>   /branches/12/channels/chan_motif.c 402686 
>   /branches/12/channels/chan_misdn.c 402686 
>   /branches/12/channels/chan_mgcp.c 402686 
>   /branches/12/channels/chan_jingle.c 402686 
>   /branches/12/channels/chan_iax2.c 402686 
>   /branches/12/channels/chan_h323.c 402686 
>   /branches/12/channels/chan_gtalk.c 402686 
>   /branches/12/channels/chan_dahdi.c 402686 
>   /branches/12/channels/chan_console.c 402686 
>   /branches/12/channels/chan_alsa.c 402686 
>   /branches/12/apps/app_voicemail.c 402686 
>   /branches/12/apps/app_userevent.c 402686 
>   /branches/12/apps/app_queue.c 402686 
>   /branches/12/apps/app_meetme.c 402686 
>   /branches/12/apps/app_disa.c 402686 
>   /branches/12/apps/app_dial.c 402686 
>   /branches/12/apps/app_confbridge.c 402687 
>   /branches/12/apps/app_agent_pool.c 402686 
>   /branches/12/addons/chan_ooh323.c 402686 
>   /branches/12/addons/chan_mobile.c 402686 
> 
> Diff: https://reviewboard.asterisk.org/r/2961/diff/
> 
> 
> Testing
> -------
> 
> As stated in the description, I ran the atxfer_threeway_nominal test in a loop. After approximately 450 test runs, there were no negative consequences. Prior to this changeset, running the test 20-50 times would result in a crash.
> 
> 
> Thanks,
> 
> Mark Michelson
> 
>

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