Linux Kernel EUVD-2026-28664

Upgrade to patched Linux kernel versions: 6.18.19 or later in the 6.18.x stable series, 6.19.9 or later in 6.19.x, or mainline kernel 7.0+. Patches are available from kernel.org stable git repositories at the referenced commit URLs (5e1ab71f74a1, b2840e33127c, 35b0c8768e84). For systems unable to immediately upgrade, disable btrfs subpage support if not required-this can be achieved by mounting btrfs filesystems with traditional page-size blocks rather than subpage configurations, though this may reduce functionality on systems with large page sizes (e.g., ARM64 with 64KB pages). Note that disabling subpage support may prevent mounting existing filesystems formatted with subpage features; test thoroughly before production deployment. As a detection control, monitor kernel logs for RCU stall warnings or hung task messages related to btrfs operations, though these symptoms may only appear under specific memory pressure or concurrent access patterns. No compensating network-level controls apply since this is a local kernel issue. The fix is a simple one-line addition to ensure proper lock release, making it low-risk to apply during standard maintenance windows.