A service provider driver which properly locks the file session driver for Laravel.
This issue was resolved with a pull request that was never integrated in the Laravel core, because the Laravel team wasn't able to reproduce it.
Some other topics regarding this issue.
Add to composer.json.
Load Service Provider in app/config/app.config, immediately after SessionServiceProvider.
Load the lockfile session provider in app/config/session.php.
'driver' => 'lockfile',