Index: sys/kern/subr_extent.c
===================================================================
RCS file: /cvsroot/src/sys/kern/subr_extent.c,v
retrieving revision 1.81
diff -u -p -r1.81 subr_extent.c
--- sys/kern/subr_extent.c	24 Jul 2017 19:56:07 -0000	1.81
+++ sys/kern/subr_extent.c	23 Aug 2017 13:21:46 -0000
@@ -131,6 +131,7 @@ extent_alloc_region_descriptor(struct ex
 	if (ex->ex_flags & EXF_FIXED) {
 		struct extent_fixed *fex = (struct extent_fixed *)ex;
 
+			if (!(ex->ex_flags & EXF_EARLY))
 		mutex_enter(&ex->ex_lock);
 		for (;;) {
 			if ((rp = LIST_FIRST(&fex->fex_freelist)) != NULL) {
@@ -141,17 +142,21 @@ extent_alloc_region_descriptor(struct ex
 				 * need to remember that information.
 				 */
 				LIST_REMOVE(rp, er_link);
-				mutex_exit(&ex->ex_lock);
+				if (!(ex->ex_flags & EXF_EARLY))
+					mutex_exit(&ex->ex_lock);
 				return (rp);
 			}
 			if (flags & EX_MALLOCOK) {
-				mutex_exit(&ex->ex_lock);
+				if (!(ex->ex_flags & EXF_EARLY))
+					mutex_exit(&ex->ex_lock);
 				goto alloc;
 			}
 			if ((flags & EX_WAITOK) == 0) {
-				mutex_exit(&ex->ex_lock);
+				if (!(ex->ex_flags & EXF_EARLY))
+					mutex_exit(&ex->ex_lock);
 				return (NULL);
 			}
+			KASSERT(mutex_owned(&ex->ex_lock));
 			ex->ex_flwanted = true;
 			if ((flags & EX_CATCH) != 0)
 				error = cv_wait_sig(&ex->ex_cv, &ex->ex_lock);
@@ -206,8 +211,10 @@ extent_free_region_descriptor(struct ext
 		}
 
  wake_em_up:
-		ex->ex_flwanted = false;
-		cv_broadcast(&ex->ex_cv);
+		if (!(ex->ex_flags & EXF_EARLY)) {
+			ex->ex_flwanted = false;
+			cv_broadcast(&ex->ex_cv);
+		}
 		return;
 	}
 
@@ -297,6 +304,8 @@ extent_create(const char *name, u_long s
 		ex->ex_flags |= EXF_FIXED;
 	if (flags & EX_NOCOALESCE)
 		ex->ex_flags |= EXF_NOCOALESCE;
+	if (flags & EX_EARLY)
+		ex->ex_flags |= EXF_EARLY;
 	return (ex);
 }
 
@@ -507,7 +516,8 @@ extent_alloc_region(struct extent *ex, u
 		return (ENOMEM);
 	}
 
-	mutex_enter(&ex->ex_lock);
+	if (!(ex->ex_flags & EXF_EARLY))
+		mutex_enter(&ex->ex_lock);
  alloc_start:
 
 	/*
@@ -545,6 +555,7 @@ extent_alloc_region(struct extent *ex, u
 			 * do so.
 			 */
 			if (flags & EX_WAITSPACE) {
+				KASSERT(!(ex->ex_flags & EXF_EARLY));
 				if ((flags & EX_CATCH) != 0)
 					error = cv_wait_sig(&ex->ex_cv,
 					    &ex->ex_lock);
@@ -556,7 +567,8 @@ extent_alloc_region(struct extent *ex, u
 					goto alloc_start;
 				mutex_exit(&ex->ex_lock);
 			} else {
-				mutex_exit(&ex->ex_lock);
+				if (!(ex->ex_flags & EXF_EARLY))
+					mutex_exit(&ex->ex_lock);
 				error = EAGAIN;
 			}
 			extent_free_region_descriptor(ex, myrp);
@@ -576,7 +588,8 @@ extent_alloc_region(struct extent *ex, u
 	 * at the beginning of the region list.  Insert ourselves.
 	 */
 	extent_insert_and_optimize(ex, start, size, flags, last, myrp);
-	mutex_exit(&ex->ex_lock);
+	if (!(ex->ex_flags & EXF_EARLY))
+		mutex_exit(&ex->ex_lock);
 	return (0);
 }
 
@@ -1042,7 +1055,8 @@ extent_free(struct extent *ex, u_long st
 			return (ENOMEM);
 	}
 
-	mutex_enter(&ex->ex_lock);
+	if (!(ex->ex_flags & EXF_EARLY))
+		mutex_enter(&ex->ex_lock);
 
 	/*
 	 * Find region and deallocate.  Several possibilities:
@@ -1125,7 +1139,8 @@ extent_free(struct extent *ex, u_long st
 	}
 
 	/* Region not found, or request otherwise invalid. */
-	mutex_exit(&ex->ex_lock);
+	if (!(ex->ex_flags & EXF_EARLY))
+		mutex_exit(&ex->ex_lock);
 	extent_print(ex);
 	printf("extent_free: start 0x%lx, end 0x%lx\n", start, end);
 	panic("extent_free: region not found");
@@ -1133,8 +1148,10 @@ extent_free(struct extent *ex, u_long st
  done:
 	if (nrp != NULL)
 		extent_free_region_descriptor(ex, nrp);
-	cv_broadcast(&ex->ex_cv);
-	mutex_exit(&ex->ex_lock);
+	if (!(ex->ex_flags & EXF_EARLY)) {
+		cv_broadcast(&ex->ex_cv);
+		mutex_exit(&ex->ex_lock);
+	}
 	return (0);
 }
 
Index: sys/sys/extent.h
===================================================================
RCS file: /cvsroot/src/sys/sys/extent.h,v
retrieving revision 1.25
diff -u -p -r1.25 extent.h
--- sys/sys/extent.h	27 Jul 2017 10:04:28 -0000	1.25
+++ sys/sys/extent.h	23 Aug 2017 13:21:47 -0000
@@ -73,8 +73,9 @@ struct extent_fixed {
 /* ex_flags; for internal use only */
 #define EXF_FIXED	__BIT(0)	/* extent uses fixed storage */
 #define EXF_NOCOALESCE	__BIT(1)	/* coalescing of regions not allowed */
+#define EXF_EARLY	__BIT(2)	/* no need to lock */
 
-#define EXF_BITS	"\20\2NOCOALESCE\1FIXED"
+#define EXF_BITS	"\20\3EARLY\2NOCOALESCE\1FIXED"
 
 /* misc. flags passed to extent functions */
 #define EX_NOWAIT	0		/* not safe to sleep */