Hello, I've hit this when deleting a large number of files inside a DomU (but I'm not sure this is related to Xen specific code). I'm using the 6.0 branch, fetched this morning (RC1), XEN3_DOMU kernel amd64 and the filesystem is FFSv2:
dev = 0x8e06, block = 454280, fs = /home panic: blkfree: freeing free block cpu0: Begin traceback... printf_nolog() at netbsd:printf_nolog ffs_blkfree_common.clone.1() at netbsd:ffs_blkfree_common.clone.1+0x2fa ffs_blkfree() at netbsd:ffs_blkfree+0x148 ffs_indirtrunc() at netbsd:ffs_indirtrunc+0x3d4 ffs_truncate() at netbsd:ffs_truncate+0x9a4 ufs_inactive() at netbsd:ufs_inactive+0x2df VOP_INACTIVE() at netbsd:VOP_INACTIVE+0x33 vrelel() at netbsd:vrelel+0x1bb ufs_remove() at netbsd:ufs_remove+0xcf VOP_REMOVE() at netbsd:VOP_REMOVE+0x37 do_sys_unlink() at netbsd:do_sys_unlink+0x104 syscall() at netbsd:syscall+0xc4 cpu0: End traceback... dump to dev 142,1 not possible rebooting...