Linux 6.19.2 Released After Boot-Crashing Bug Forces Emergency Patch

Linux 6.19.2 was rushed out today after Linux 6.19.1 introduced a critical boot-breaking bug that left many systems unable to start. The issue stemmed from a seemingly innocuous back-port of device_lock enforcement for driver_match_device() that inadvertently broke boot sequences across diverse hardware configurations.

The Bug That Broke Boot

The problematic change was intended to improve driver safety by enforcing device_lock during device matching operations. However, this core driver modification wasn't properly back-ported alongside all the necessary supporting fixes. As Greg Kroah-Hartman explained in the patch reverting the change, "It causes boot regressions on some systems as all of the 'fixes' for drivers are not properly backported yet."

This single change became the sole code modification between Linux 6.19.1 and 6.19.2, highlighting how even minor driver changes can have catastrophic effects when dependencies aren't fully accounted for.

LTS Kernels Also Affected

The bug's impact extended beyond the main development kernel. Linux 6.18.12, Linux 6.12.73, and Linux 6.6.126 all received emergency releases to revert the same problematic code. This widespread impact demonstrates how changes in core driver infrastructure can ripple through multiple kernel branches.

Technical Details

The device_lock enforcement was meant to prevent race conditions during driver binding, but the incomplete back-port meant that related driver fixes weren't present to handle the new locking requirements. This created a situation where the kernel would hang or crash during the boot process when attempting to match devices to drivers.

Kroah-Hartman's cautious approach in the patch notes suggests waiting "a few -rc releases first" before reconsidering such core changes, given the "potential for explosions" when modifying fundamental driver infrastructure.

Impact and Resolution

Affected users can now download Linux 6.19.2 from the kernel mailing list, which restores normal boot functionality by reverting the problematic device_lock enforcement. The quick turnaround from 6.19.1 to 6.19.2 demonstrates the kernel development team's responsiveness to critical issues, though it also highlights the risks inherent in back-porting complex driver changes.

The incident serves as a reminder of the delicate balance between security improvements and system stability in kernel development, particularly when changes affect core driver infrastructure that touches virtually every hardware component in a system.