Mainline update: filesystem reliability, IOMMU fixes, and a leaner kallsyms

A round of XFS, btrfs, and erofs fixes; AMD IOMMU and PowerPC corrections; and kallsyms/kbuild cleanups.

#Btrfs #Erofs #IOMMU #Kallsyms #PowerPC #Xfs

https://kerneldispatch.com/posts/mainline-2026-09-13