svn commit: r354785 - head/sys/vm

[Doug Moore]

Author: dougm
Date: Sun Nov 17 06:50:36 2019
New Revision: 354785
URL: https://svnweb.freebsd.org/changeset/base/354785

Log:
  The loop in vm_map_protect that verifies that all transition map
  entries are stabilized, repeatedly verifies the same entry. Check each
  entry in turn.
  
  Reviewed by: kib (code only), alc
  Tested by: pho
  MFC after: 7 days
  Differential Revision: https://reviews.freebsd.org/D22405

Modified:
  head/sys/vm/vm_map.c

Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c	Sun Nov 17 03:54:31 2019	(r354784)
+++ head/sys/vm/vm_map.c	Sun Nov 17 06:50:36 2019	(r354785)
@@ -2469,17 +2469,16 @@ again:
 			vm_map_unlock(map);
 			return (KERN_PROTECTION_FAILURE);
 		}
-		if ((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0)
-			in_tran = entry;
+		if ((current->eflags & MAP_ENTRY_IN_TRANSITION) != 0)
+			in_tran = current;
 	}
 
 	/*
-	 * Postpone the operation until all in transition map entries
-	 * are stabilized.  In-transition entry might already have its
-	 * pages wired and wired_count incremented, but
-	 * MAP_ENTRY_USER_WIRED flag not yet set, and visible to other
-	 * threads because the map lock is dropped.  In this case we
-	 * would miss our call to vm_fault_copy_entry().
+	 * Postpone the operation until all in-transition map entries have
+	 * stabilized.  An in-transition entry might already have its pages
+	 * wired and wired_count incremented, but not yet have its
+	 * MAP_ENTRY_USER_WIRED flag set.  In which case, we would fail to call
+	 * vm_fault_copy_entry() in the final loop below.
 	 */
 	if (in_tran != NULL) {
 		in_tran->eflags |= MAP_ENTRY_NEEDS_WAKEUP;