kib 732157ce21 Vm map code performs clipping when map entry covers region which is
larger than the operational region.  If the op region size is zero,
clipping would create a zero-sized map entry.  The result is that vm
map splay starts behaving inconsistently, sometimes returning
zero-sized entry, sometimes the next (or previous) entry.

One step further, it could result in e.g. vm_map_wire() setting
MAP_ENTRY_IN_TRANSITION on the zero-sized entry, but failing to clear
it in the done part.  The vm_map_delete() than hangs forever waiting
for the flag removal.

Verify for zero-length requests and act as if it is always successfull
without performing any action on the address space.

Diagnosed by:	pho
Tested by:	pho (previous version)
Reviewed by:	alc (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
2013-11-20 09:03:48 +00:00
..