svn commit: r257680 - head/sys/vm

[Konstantin Belousov]

Author: kib
Date: Tue Nov  5 06:18:50 2013
New Revision: 257680
URL: http://svnweb.freebsd.org/changeset/base/257680

Log:
  Do not coalesce if the swap object belongs to tmpfs vnode.  The
  coalesce would extend the object to keep pages for the anonymous
  mapping created by the process.  The pages has no relations to the
  tmpfs file content which could be written into the corresponding
  range, causing anonymous mapping and file content aliasing and
  subsequent corruption.
  
  Another lesser problem created by coalescing is over-accounting on the
  tmpfs node destruction, since the object size is substracted from the
  total count of the pages owned by the tmpfs mount.
  
  Reported and tested by:	bdrewery
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/vm/vm_object.c

Modified: head/sys/vm/vm_object.c
==============================================================================
--- head/sys/vm/vm_object.c	Tue Nov  5 06:13:46 2013	(r257679)
+++ head/sys/vm/vm_object.c	Tue Nov  5 06:18:50 2013	(r257680)
@@ -2099,8 +2099,9 @@ vm_object_coalesce(vm_object_t prev_obje
 	if (prev_object == NULL)
 		return (TRUE);
 	VM_OBJECT_WLOCK(prev_object);
-	if (prev_object->type != OBJT_DEFAULT &&
-	    prev_object->type != OBJT_SWAP) {
+	if ((prev_object->type != OBJT_DEFAULT &&
+	    prev_object->type != OBJT_SWAP) ||
+	    (prev_object->flags & OBJ_TMPFS) != 0) {
 		VM_OBJECT_WUNLOCK(prev_object);
 		return (FALSE);
 	}