[SR-Users] unexpected behavior of save from registrar module

[Vasiliy Ganchev]

Hi Sebastian!

Thanks for your response!

In our system we have:
- usrloc with db_mode=1 (Write-Through scheme. All changes to usrloc are
immediately reflected in database too. )
- sqlite DB, to store location info (sqlite is blocking for the time of
write, and if there are 2 write attempts by 2 workers - one of them fails)

In this scheme - I definitely need to process only one REGISTER at the same
time (In our setup kamailio are not high loaded)

And locking - seemed to me the safest workaround for production (as turned
out - it did not).

What I am doing now - is testing my kamailio with usrloc db_mode=2
(Write-Back scheme.) (and this is going to be production solution soon)

I posted the topic - to discuss my case - and make some changes (sources or
documentation) - to prevent someone else in future to encounter something
similar. 

cheers

a registrar module working 

Sebastian Damm-2 wrote
> Hi,
> 
> indeed, when a function returns with 0, Kamailio immediately ends the
> processing of the packet. So that's why the unlock statement is never
> executed.
> 
> I am wondering, why you are using locks at this point. That way, only
> one REGISTER can be processed at the same time, since they all share
> the same lock. I've never seen somebody do this before, and multiple
> REGISTERs being processed in parallel should be no problem. What
> problem do you try to solve by surrounding the save command with
> locks?
> 
> Best Regards,
> Sebastian
> 
> On Thu, Oct 12, 2017 at 6:03 PM, Vasiliy Ganchev <

> vancecezar@

> > wrote:
>> Hi, community!
>>
>> I have in my Kamailio script following block (while REGISTER processing,
>> after auth succeed):
>>
>>  .....
>>         /* Save to usrloc */
>>         lock("LOCATION_LOCK");
>>         if (!save("location")) {
>>                 unlock("LOCATION_LOCK");
>>                 sl_reply_error();
>>                 exit();
>>         }
>>         unlock("LOCATION_LOCK");
>>
>> ......
>>
>> According to module documentation - if "save" - failed (for any reason) -
>> I
>> expected the control to be returned to the script with error code "-1"
>>
>> But, there are cases - when this does not happen - which lead to deadlock
>> for workers processing REGISTERs (I never unlock("LOCATION_LOCK")):
>> - module answers with internal error - and return 0 from "save" function:
>> https://github.com/kamailio/kamailio/blob/master/src/modules/registrar/save.c
>> - line 1013
>>
>> My use case happened due to malfunctioning device that in some moment of
>> time:
>> - send REGISTER update
>> - kamailio answers 200OK
>> - device retransmit the same REGISTER (same CSeq)
>> - during 20 seconds (hardcoded value in registrar module) - kamailio
>> answers
>> 200OK (and everything is ok)
>> - if retransmission continue more than 20s - kamailio answered 400 Bad
>> request, and did not return control to script (as a result I had no
>> chance
>> to unlock("LOCATION_LOCK") from code above)
>>
>> Tested it on kamailio 4.2.5 and 5.0.3.
>>
>> as for me, possible solutions are:
>> - return -1 instead of 0 from "save" by default
>> - if there are some reasons not to do this - we should change
>> documentation,
>> and explicitly mention that there are cases - when script execution is
>> stopped.
>>
>> thanks in advance!
>>
>> cheers
>>
>>
>>
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