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Date:      Sun, 8 Sep 2013 17:51:22 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r255396 - in head/sys: kern vm
Message-ID:  <201309081751.r88HpM0s047151@svn.freebsd.org>
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Author: kib
Date: Sun Sep  8 17:51:22 2013
New Revision: 255396
URL: http://svnweb.freebsd.org/changeset/base/255396

Log:
  Drain for the xbusy state for two places which potentially do
  pmap_remove_all(). Not doing the drain allows the pmap_enter() to
  proceed in parallel, making the pmap_remove_all() effects void.
  
  The race results in an invalidated page mapped wired by usermode.
  
  Reported and tested by:	pho
  Reviewed by:	alc
  Sponsored by:	The FreeBSD Foundation
  Approved by:	re (glebius)

Modified:
  head/sys/kern/vfs_bio.c
  head/sys/vm/vm_object.c

Modified: head/sys/kern/vfs_bio.c
==============================================================================
--- head/sys/kern/vfs_bio.c	Sun Sep  8 17:47:14 2013	(r255395)
+++ head/sys/kern/vfs_bio.c	Sun Sep  8 17:51:22 2013	(r255396)
@@ -1693,6 +1693,12 @@ brelse(struct buf *bp)
 
 				KASSERT(presid >= 0, ("brelse: extra page"));
 				VM_OBJECT_WLOCK(obj);
+				while (vm_page_xbusied(m)) {
+					vm_page_lock(m);
+					VM_OBJECT_WUNLOCK(obj);
+					vm_page_busy_sleep(m, "mbncsh");
+					VM_OBJECT_WLOCK(obj);
+				}
 				if (pmap_page_wired_mappings(m) == 0)
 					vm_page_set_invalid(m, poffset, presid);
 				VM_OBJECT_WUNLOCK(obj);

Modified: head/sys/vm/vm_object.c
==============================================================================
--- head/sys/vm/vm_object.c	Sun Sep  8 17:47:14 2013	(r255395)
+++ head/sys/vm/vm_object.c	Sun Sep  8 17:51:22 2013	(r255396)
@@ -1910,6 +1910,12 @@ again:
 		 * not specified.
 		 */
 		vm_page_lock(p);
+		if (vm_page_xbusied(p)) {
+			VM_OBJECT_WUNLOCK(object);
+			vm_page_busy_sleep(p, "vmopax");
+			VM_OBJECT_WLOCK(object);
+			goto again;
+		}
 		if ((wirings = p->wire_count) != 0 &&
 		    (wirings = pmap_page_wired_mappings(p)) != p->wire_count) {
 			if ((options & (OBJPR_NOTWIRED | OBJPR_NOTMAPPED)) ==

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