Segfaults in php agent module / sleepResumingAfterInterruption()

[keeshoekzema]

Describe the bug
When using the apm-agent-php module on a busy server, the agent sometimes crashes with a segfault.

To Reproduce
(Un)fortunately, the error doesn't appear very often. But it seems to be a recursive loop. This one was caught twice in ~3 days
My relevant configuration:
elastic_apm.server_url="http://localhost:8200/"
elastic_apm.transaction_ignore_urls=/healthcheck*
elastic_apm.transaction_sample_rate=0.1
elastic_apm.profiling_inferred_spans_enabled=true
elastic_apm.verify_server_cert = false

I'm using modphp8.1.17 and apm-agent-php 1.8.1

Expected behavior
No segfaults

A gdb bt from the core:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f962369c6cf in time_nanosleep_resuming_after_interruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
[Current thread is 1 (Thread 0x7f962b638c40 (LWP 3480716))]
#0  0x00007f962369c6cf in time_nanosleep_resuming_after_interruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#1  0x00007f962369c116 in sleepResumingAfterInterruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#2  0x00007f962369cab5 in time_nanosleep_resuming_after_interruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#3  0x00007f962369c116 in sleepResumingAfterInterruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#4  0x00007f962369cab5 in time_nanosleep_resuming_after_interruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#5  0x00007f962369c116 in sleepResumingAfterInterruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#6  0x00007f962369cab5 in time_nanosleep_resuming_after_interruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
[ .. some time later .. ]
#45510 0x00007f962369cab5 in time_nanosleep_resuming_after_interruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#45511 0x00007f962369c116 in sleepResumingAfterInterruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#45512 0x00007f962369cab5 in time_nanosleep_resuming_after_interruption () from /opt/elastic/apm-agent-php/extensions/elastic_apm-20210902.so
#45513 0x00007f962a759ae9 in execute_ex () from /usr/lib/apache2/modules/libphp8.1.so
#45514 0x00007f962a75cd8d in zend_execute () from /usr/lib/apache2/modules/libphp8.1.so
#45515 0x00007f962a6ec845 in zend_execute_scripts () from /usr/lib/apache2/modules/libphp8.1.so
#45516 0x00007f962a68968a in php_execute_script () from /usr/lib/apache2/modules/libphp8.1.so
#45517 0x00007f962a7d5690 in ?? () from /usr/lib/apache2/modules/libphp8.1.so
#45518 0x000055ecc2b17ae8 in ap_run_handler ()
#45519 0x000055ecc2b18096 in ap_invoke_handler ()
#45520 0x000055ecc2b2fb7e in ap_internal_redirect ()
#45521 0x00007f962b017bfc in ?? () from /usr/lib/apache2/modules/mod_rewrite.so
#45522 0x000055ecc2b17ae8 in ap_run_handler ()
#45523 0x000055ecc2b18096 in ap_invoke_handler ()
#45524 0x000055ecc2b30863 in ap_process_async_request ()
#45525 0x000055ecc2b30a32 in ap_process_request ()
#45526 0x000055ecc2b2cac6 in ?? ()
#45527 0x000055ecc2b21828 in ap_run_process_connection ()
#45528 0x00007f962b557997 in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
#45529 0x00007f962b557c9a in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
#45530 0x00007f962b558a18 in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
#45531 0x000055ecc2af9488 in ap_run_mpm ()
#45532 0x000055ecc2af1499 in main ()

[intuibase]

Hey @keeshoekzema

Thank you for reporting issue.
Is it possible to deliver us reproduction environment like docker image, virtual machine, etc?

Regards,
Pawel

[keeshoekzema]

Unfortunately i'm not able to reproduce it in a test environment as this server is doing ~150 requests per second and i only saw this segfault a few times in the span of 3 days.