From 5944426158880baf8b40d31b26fd23add753dd93 Mon Sep 17 00:00:00 2001
From: mpi <mpi@openbsd.org>
Date: Sat, 22 May 2021 08:38:29 +0000
Subject: [PATCH] Use atomic operations for reference counting VM maps.

This is necessary to do this accounting without the KERNEL_LOCK().

ok mvs@, kettenis@
---
 sys/uvm/uvm_map.c | 15 ++++++++-------
 sys/uvm/uvm_map.h |  5 +++--
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/sys/uvm/uvm_map.c b/sys/uvm/uvm_map.c
index c3d9190ca78..459045b01f1 100644
--- a/sys/uvm/uvm_map.c
+++ b/sys/uvm/uvm_map.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_map.c,v 1.274 2021/03/26 13:40:05 mpi Exp $	*/
+/*	$OpenBSD: uvm_map.c,v 1.275 2021/05/22 08:38:29 mpi Exp $	*/
 /*	$NetBSD: uvm_map.c,v 1.86 2000/11/27 08:40:03 chs Exp $	*/
 
 /*
@@ -491,12 +491,13 @@ uvm_mapent_addr_remove(struct vm_map *map, struct vm_map_entry *entry)
 /*
  * uvm_map_reference: add reference to a map
  *
- * XXX check map reference counter lock
+ * => map need not be locked
  */
-#define uvm_map_reference(_map)						\
-	do {								\
-		map->ref_count++;					\
-	} while (0)
+void
+uvm_map_reference(struct vm_map *map)
+{
+	atomic_inc_int(&map->ref_count);
+}
 
 /*
  * Calculate the dused delta.
@@ -4292,7 +4293,7 @@ uvm_map_deallocate(vm_map_t map)
 	int c;
 	struct uvm_map_deadq dead;
 
-	c = --map->ref_count;
+	c = atomic_dec_int_nv(&map->ref_count);
 	if (c > 0) {
 		return;
 	}
diff --git a/sys/uvm/uvm_map.h b/sys/uvm/uvm_map.h
index 531d6f2ef06..12092ebfcd2 100644
--- a/sys/uvm/uvm_map.h
+++ b/sys/uvm/uvm_map.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_map.h,v 1.69 2021/03/12 14:15:49 jsg Exp $	*/
+/*	$OpenBSD: uvm_map.h,v 1.70 2021/05/22 08:38:29 mpi Exp $	*/
 /*	$NetBSD: uvm_map.h,v 1.24 2001/02/18 21:19:08 chs Exp $	*/
 
 /*
@@ -259,6 +259,7 @@ RBT_PROTOTYPE(uvm_map_addr, vm_map_entry, daddrs.addr_entry,
  * read_locks and write_locks are used in lock debugging code.
  *
  *  Locks used to protect struct members in this file:
+ *	a	atomic operations
  *	I	immutable after creation or exec(2)
  *	v	`vm_map_lock' (this map `lock' or `mtx')
  */
@@ -272,7 +273,7 @@ struct vm_map {
 	struct uvm_map_addr	addr;		/* [v] Entry tree, by addr */
 
 	vsize_t			size;		/* virtual size */
-	int			ref_count;	/* Reference count */
+	int			ref_count;	/* [a] Reference count */
 	int			flags;		/* flags */
 	struct mutex		flags_lock;	/* flags lock */
 	unsigned int		timestamp;	/* Version number */
-- 
2.20.1