[sr-dev] [kamailio/kamailio] crash in slow timer (#2120)

[lazedo]

<!--
Kamailio Project uses GitHub Issues only for bugs in the code or feature requests. Please use this template only for bug reports.

If you have questions about using Kamailio or related to its configuration file, ask on sr-users mailing list:

  * http://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

If you have questions about developing extensions to Kamailio or its existing C code, ask on sr-dev mailing list:

  * http://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-dev

Please try to fill this template as much as possible for any issue. It helps the developers to troubleshoot the issue.

If there is no content to be filled in a section, the entire section can be removed.

You can delete the comments from the template sections when filling.

You can delete next line and everything above before submitting (it is a comment).
-->

### Description

on busy servers, there's a sporadic crash in slow timer.
we don't have any debugging data anymore nor a way to reliably reproduce it.
just posting here in case someone sees the same and can find a way to reliably reproduce it and maybe test the patch below.
<!--
Explain what you did, what you expected to happen, and what actually happened.
-->

### Troubleshooting

#### Reproduction

<!--
If the issue can be reproduced, describe how it can be done.
-->


### Possible Solutions

<!--
If you found a solution or workaround for the issue, describe it. Ideally, provide a pull request with a fix.
-->
 with the patch below we don't see any crashes
either `tl` or `tl->f` is null when it crashes. this is probably some race condition
```
diff --git a/src/core/timer.c b/src/core/timer.c
index 0e0dc8812..3c59db3da 100644
--- a/src/core/timer.c
+++ b/src/core/timer.c
@@ -1128,7 +1128,7 @@ void slow_timer_main()
 #endif
 				SET_RUNNING_SLOW(tl);
 				UNLOCK_SLOW_TIMER_LIST();
-					ret=tl->f(*ticks, tl, tl->data);
+					ret= (tl->f ? tl->f(*ticks, tl, tl->data) : 0);
 					/* reset the configuration group handles */
 					cfg_reset_all();
 					if (ret==0){
```
### Additional Information

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

```
5.1 / 5.2
```

* **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`)
-->

```
CentOS7
```


-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/kamailio/kamailio/issues/2120
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.kamailio.org/pipermail/sr-dev/attachments/20191031/52cb985f/attachment-0001.html>