srsepc context management disodrer and S-MAC invalid problem

[copslock]

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Issue Description

[Describe the issue in detail] 1.The srsEPC keeps performing invalid Short-MAC symptom since 18.06(I think same problem exist in early versions too),if the UE entered IDLE mode for a while,when sending Service Request to the EPC,it will complain about invalid S-MAC and attach reject 2.Due the failure in Service Request procedure in 1,the nas->ctx seems failed to release the current thread that caused the context cannot be released properly,which caused in the latter PDN reattch procedure the ATTACH ACCEPT message cannot update to the last PDN attach procedure ENB-UE-S1AP-id(still using the un-released id in Service Request procedure),But I don't understand why the SPGW Allocated IP 172.16.0.2 to IMSI 000000000000000 pointer is null,I think it should at least reads the last IMSI in Service Request,maybe due to the invalid Service Request handling the pointer data was cleared

Setup Details

[Specify details of the test setup. This would help us reproduce the problem reliably] e.g. Network configuration, Operation System, Hardware, RF front-end, library and driver versions COTS UE -> COTS eNodeB -> srsEPC

Expected Behavior

[What you expect to happen]

Actual Behaviour

[What happens instead e.g. error message]

Steps to reproduce the problem

[Tell us how to reproduce this issue e.g. RF setup, application config files]

Additional Information

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##fix routine## 1.find the root cause of invalid S-MAC 2.properly release invaild(unfinished) procedure context pointer 3.something wrong in ENB-UE-S1AP-id global management.

[copslock]

I think I have found the root cause of NULL pointer in initial context attach accept now,but the S-MAC invaild problem needs more time to investigate