[asterisk-dev] [Code Review] 3548: suspended destructions of pri spans following PRI_EVENT_REMOVED

[rmudgett]

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/trunk/channels/chan_dahdi.c
<https://reviewboard.asterisk.org/r/3548/#comment22199>

    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.



/trunk/channels/sig_pri.c
<https://reviewboard.asterisk.org/r/3548/#comment22200>

    guidelines.  Function curly on its own line.


- rmudgett


On June 16, 2014, 11:07 a.m., Tzafrir Cohen wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/3548/
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> 
> (Updated June 16, 2014, 11:07 a.m.)
> 
> 
> Review request for Asterisk Developers and rmudgett.
> 
> 
> Bugs: ASTERISK-23554
>     https://issues.asterisk.org/jira/browse/ASTERISK-23554
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> Repository: Asterisk
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> Description
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> 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:
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> 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.
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> 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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> 
> Diffs
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>   /trunk/channels/sig_pri.c 416393 
>   /trunk/channels/sig_pri.h 416393 
>   /trunk/channels/chan_dahdi.c 416393 
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> Diff: https://reviewboard.asterisk.org/r/3548/diff/
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> 
> Testing
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> Thanks,
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> Tzafrir Cohen
> 
>

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