zfs + sendfile: do not produce partially valid pages for vnode's tail

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

0 files changed, 0 insertions, 0 deletions