Mass segfaults on a ZFS host: not bad RAM, an unsigned underflow in zfs_fillpage()

A host that answers on no port while the kernel keeps logging is not failing memory. In OpenZFS before 2.4.4 and 2.3.9, zfs_fillpage() computes io_len = i_size - io_off in unsigned types: race an mmap read against an in-place truncate and the length underflows, so dmu_read() zero-fills physical memory far past the page. Fixed on 21 August 2026 in 2.4.4 and 2.3.9 — but not in 2.2.11, released the same minute.