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php-fpm segmentation fault when sending the reload signal to php-fpm in a Docker container #1485

Open claude-vessaz-hs opened 3 years ago

claude-vessaz-hs commented 3 years ago

Frequently asked questions

Describe the bug php-fpm receives a SIGSEV when a reload signal (kill -HUP <pid>) is sent to any of the php-fpm processes. So far, I was only able to reproduce this behaviour in a docker container. I was able to reproduce the error in a debug container:

(16:02 0fd9a2343028:/ebs1/www) gdb /usr/sbin/php-fpm7.0
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Reading symbols from /usr/sbin/php-fpm7.0...Reading symbols from /usr/lib/debug/.build-id/9c/f28673850581d357ef1693f98fdd02117c208c.debug...done.
done.
(gdb) r --fpm-config /etc/php/7.0/fpm/php-fpm.conf
Starting program: /usr/sbin/php-fpm7.0 --fpm-config /etc/php/7.0/fpm/php-fpm.conf
warning: Error disabling address space randomization: Operation not permitted
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[27-Nov-2020 16:03:48] NOTICE: fpm is running, pid 126
[27-Nov-2020 16:03:49] NOTICE: ready to handle connections
[27-Nov-2020 16:03:49] NOTICE: systemd monitor interval set to 10000ms

Program received signal SIGSEGV, Segmentation fault.
fpm_event_select_wait (queue=<optimized out>, timeout=<optimized out>) at ./sapi/fpm/fpm/events/select.c:120
120 ./sapi/fpm/fpm/events/select.c: No such file or directory.
(gdb) bt
#0  fpm_event_select_wait (queue=<optimized out>, timeout=<optimized out>) at ./sapi/fpm/fpm/events/select.c:120
#1  0x0000564b4b2fe439 in fpm_event_loop (err=err@entry=0) at ./sapi/fpm/fpm/fpm_events.c:416
#2  0x0000564b4b2f8c07 in fpm_run (max_requests=0x7ffef3d1a85c) at ./sapi/fpm/fpm/fpm.c:115
#3  0x0000564b4b0dd311 in main (argc=3, argv=0x7ffef3d1ae78) at ./sapi/fpm/fpm/fpm_main.c:1881

This started happening after the latest upgrade of php7.0-fpm (and a bunch of other packages) to the -37 version. We did not observe this behaviour in previous versions (-34 and lower). It was not able to reproduce the behaviour by just installing php-fpm, so I suspect it is related to one of our extensions, but I was not able to narrow it down yet which one.

While this bug-report is about PHP 7.0, it affects 7.3 as well, but I can't say for sure if it was introduced recently in the 7.3 version.

To Reproduce I unfortunately was only able to reproduce it in a container depending on internal resources so far and I could not narrow down what extension is causing this. I am currently working on a container which only depends on public resources and will comment in the issue as soon I have a Dockerfile avilable.

In a nutshell:

  1. Start php-fpm process
  2. Send reload signal (kill -HUP <any php-fpm pid>
  3. Observe segfault

Expected behavior php-fpm should reload without a segfault.

Distribution (please complete the following information):

Package(s) (please complete the following information):

php7.0-fpm
php7.0-bcmath
php7.0-cli
php7.0-gd
php7.0-mysql
php7.0-curl
php7.0-dev
php7.0-apcu
php7.0-apcu-bc
php7.0-gearman
php7.0-geoip
php7.0-intl
php7.0-memcached
php7.0-mongodb
php7.0-mbstring
php7.0-oauth
php7.0-redis
php7.0-xdebug
php7.0-xml
php7.0-zip
php7.0-zmq
grpc-1.25.0 from pecl
protobuf from https://github.com/hootsuite/php-protobuf
maxmind-db-reader-1.6.0 from https://github.com/maxmind/MaxMind-DB-Reader-php
claude-vessaz-hs commented 3 years ago

I was finally able to narrow this down and create a "simple" Dockerfile for reproduction: https://gist.github.com/claude-vessaz-hs/7cf49137435db2036eaa70d318e27a2e

Full reproduction steps:

  1. Copy both files from gist into directory
  2. Open path in terminal
  3. docker build -t php-fpm70:segfault .
  4. docker run --rm --name segfault php-fpm70:segfault
  5. Open a new terminal window and exec into container: docker exec -it segfault bash
  6. Look up PID of php-fpm process (ps aux)
  7. Send reload command: kill -HUP <pid>
  8. Container should exit with a segfault

The issue boils down to events.mechanism = select in the php-fpm config. We have this enabled. If the line is commented out, the php-fpm process reloads fine.

I was not able to install an older version of php-fpm and see if it really was introduced with the latest update.