Since r212650 and before this change sendfile(2) could produce a partially valid page for a trailing portion of a ZFS vnode. vm_fault() always wants to see a fully valid page even if it's the last page that partially extends beyond vnode's end. Otherwise it calls vop_getpages() to bring in the page. In the case of ZFS this means that the data is read from the page into the same page and this breaks checks in ZFS mappedread() - a thread that set VPO_BUSY on the page in vm_fault() will get blocked forever waiting for it to be cleared. Many thanks to Kai and Jeremy for reproducing the issue and providing important debugging information and help. Reported by: Kai Gallasch <gallasch@free.de>, Jeremy Chadwick <freebsd@jdc.parodius.com> Tested by: Kai Gallasch <gallasch@free.de>, Jeremy Chadwick <freebsd@jdc.parodius.com> Reviewed by: kib MFC after: 3 days To-Do: apply the same treatment to tmpfs + sendfile