Fix perl_exec_simple memory leak

[p120ph37]

Summary

Fix a memory leak in the perl module that can accumulate OS malloc'd memory over time. The leak is fairly slow, so unless your configuration makes very heavy use of perl functions, it may go unnoticed for quite a while, but it can eventually result in OS memory exhaustion and the OOM-killer.

Details

perl_exec_simple has a memory leak because call_argv doesn't garbage-collect its arguments properly. This is technically a Perl bug, and is tracked here: Perl/perl5#22255 But, until it is fixed in Perl, we should work around the issue from the OpenSIPS side.

See #3402 for more details on how to reproduce the bug in OpenSIPS and how to validate the fix.

Solution

This PR fixes the problem by applying the appropriate Perl garbage-collection context markers around the function call so that garbage collection of the arguments happens as control returns to the caller.

Compatibility

No functional change to OpenSIPS.

Closing issues

closes #3402

[liviuchircu]

Hi @p120ph37! I took a quick look at the push_scope(), pop_scope() internals, coupled w/ Perl_savetmps() and Perl_free_tmps() and they seem to be quite harmless - if adding this scope management fixes the leak for you, I am more than happy to merge & backport all the way down to 3.2. Cheers!