[sr-dev] [kamailio/kamailio] Kamailio freezes with DMQ and dialog (#2535)

[pwakano]

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### Description

When running a load test Kamailio eventually becames unresponsive and stops processing calls.
Kamilio is configured to use the DMQ replication for dialog and usrloc. Also the dialog keepalived is enabled.


### Troubleshooting

>From investigation, the problem happens faster and easier when there is some network degradation causing packet loss and/or retransmissions but even without any noticeable network issue the freeze eventually happens. 

#### Reproduction

Run a simple load test making calls at a rate of ~5 cps and keep around ~2000 calls connected all the time. A higher cps seems to make it easier to reproduce the problem.
Adding network degradation to the environment makes the problem happens, but when running a tool such as SIPp for the load test, the retransmission can be forced by simply killing the SIPp instance receiving calls which will then force Kamailio to retransmit.

#### Debugging Data

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Output of kamct trap:
[gdb_kamailio_20201028_213030.txt](https://github.com/kamailio/kamailio/files/5455020/gdb_kamailio_20201028_213030.txt)

#### Log Messages

Local generated requests shows up in the log, but are not sent in the network


### Possible Solutions

Not found so far

### Additional Information

  * **Kamailio Version** - output of `kamailio -v`

```
# kamailio -v
version: kamailio 5.4.2 (x86_64/linux) c3b91f
flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES
ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB
poll method support: poll, epoll_lt, epoll_et, sigio_rt, select.
id: c3b91f 
compiled on 13:50:37 Oct 27 2020 with gcc 4.8.5
```

* **Operating System**:

<!--
Details about the operating system, the type: Linux (e.g.,: Debian 8.4, Ubuntu 16.04, CentOS 7.1, ...), MacOS, xBSD, Solaris, ...;
Kernel details (output of `uname -a`)
-->

```
# cat /etc/centos-release
CentOS Linux release 7.8.2003 (Core)
# uname -a
Linux hostname 3.10.0-1127.19.1.el7.x86_64 #1 SMP Tue Aug 25 17:23:54 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
```


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