svn commit: r352800 - head/sys/vm

[Mark Johnston]

Author: markj
Date: Fri Sep 27 16:41:34 2019
New Revision: 352800
URL: https://svnweb.freebsd.org/changeset/base/352800

Log:
  Fix object locking in vm_object_unwire() after r352174.
  
  Now, vm_page_busy_sleep() expects the page's object to be locked.
  vm_object_unwire() does some unusual lazy locking of the object chain
  and keeps objects locked until a busy page is encountered or the loop
  terminates.  When a busy page is encountered, rather than unlocking all
  but the "bottom-level" object, we must instead skip the object to which
  "tm" belongs.
  
  Reported and tested by:	pho
  Reviewed by:	kib
  Discussed with:	jeff
  Sponsored by:	Intel, Netflix
  Differential Revision:	https://reviews.freebsd.org/D21790

Modified:
  head/sys/vm/vm_object.c

Modified: head/sys/vm/vm_object.c
==============================================================================
--- head/sys/vm/vm_object.c	Fri Sep 27 16:35:08 2019	(r352799)
+++ head/sys/vm/vm_object.c	Fri Sep 27 16:41:34 2019	(r352800)
@@ -2169,10 +2169,11 @@ again:
 			m = TAILQ_NEXT(m, listq);
 		}
 		if (vm_page_xbusied(tm)) {
-			for (tobject = object; locked_depth > 1;
+			for (tobject = object; locked_depth >= 1;
 			    locked_depth--) {
 				t1object = tobject->backing_object;
-				VM_OBJECT_RUNLOCK(tobject);
+				if (tm->object != tobject)
+					VM_OBJECT_RUNLOCK(tobject);
 				tobject = t1object;
 			}
 			vm_page_busy_sleep(tm, "unwbo", true);