String corruption on deployments with php-fpm 8.1.6

Description

Hello,

We experience seemingly random in-memory corruption of code when deploying new versions of our PHP app on php-fpm 8.1.6 on Linux. Here is a sample error message:

include(/space/www/api2019/data/releases/20220607140425/vendor/la�R�F): Failed to open stream: No such file or directory

This example happens in the class loader from composer. The beginning of the file name is correct, the end is obviously not.

Another example (another release on another server):

Call to undefined function Symfony\Component\HttpFoundation\implode()

This bug is not easily reproducible, it happens in random-looking places in the code, sometimes but not always, on some servers but not others (we have 10 app servers, the bug appears on one server at a time, very rarely two, not on every release but more than half of them).

When it happens, it looks like there is only one corrupted chunk of data; depending on the affected data, it may only cause a few real errors or basically prevent the code from working on the server at all. It generates errors for a few minutes. Restarting the fpm daemon fixes it; reloading it or running opcache_reset() does not.

We will try to reproduce it on a staging server; at the moment I can only say it appears under load and not under light testing.

It may or may not be related to #8731 (same app, same servers, seemingly fixed by downgrading to 8.0.19).

I know this report is not really helpful, but I'm at a loss how to make it more useful.

Downgrading to PHP 8.0.19 seems to fix the issue.

PHP Version

PHP 8.1.6 (cli) (built: May 17 2022 16:49:19) (NTS)

Operating System

Debian 10

まず、Debian 10 上で PHP-FPM 8.1.6 を実行している負荷のかかったステージングサーバーで破損の再現を試み、PHP 8.0.19 の場合と比較します。FPM の再起動、リロード、または opcache_reset() の実行によって結果が変わるかを観察し、Composer ClassLoader の失敗と #8731 との関連の可能性を確認します。再現可能な原因を特定し、検証済みの修正を確認できれば完了です。