Linux Kernel: Cache Policy Race Condition and Minor Subsystem Updates

Transcript

Good morning, this is your Linux Kernel briefing for June 2nd, 2026.

Today's activity centers on a significant concurrency fix in the device mapper subsystem, along with targeted improvements to auxiliary display drivers.

The most critical change addresses a race condition in the SMQ cache policy that could lead to data corruption. The issue, fixed in commit d3f0a60, stems from improper locking around allocation checks during cache invalidation. When multiple threads attempt to invalidate the same cache entry simultaneously, they can both observe the entry as allocated before acquiring the necessary lock. This creates a check-then-act race where the second invalidator operates on stale data, potentially corrupting SMQ queues or hash tables, and even triggering allocation errors when entries are freed twice.

The fix moves the allocation check inside the existing invalidate lock, ensuring that the predicate check and destructive operations are properly serialized. This builds on previous locking improvements from commit 2d1f7b65f5de, demonstrating the iterative nature of concurrent programming fixes in complex subsystems like device mapper.

On the auxiliary display front, Linus merged a small but important set of updates addressing boundary conditions. The changes include a fix for out-of-bounds reads when zero-length messages are stored in the line display library, plus routine refactoring in the Max6959 driver and Kconfig cleanup. Linus noted these updates are so minimal that merging them now creates less work than scheduling them for a later release.

For developers working with device mapper caching, this race condition fix should improve system stability under high concurrency. The auxiliary display changes primarily affect embedded developers working with character displays and panel interfaces.

That's your kernel update for today. We'll be back tomorrow with more from the development front.