[src/trunk]: src/sys/dev/dm dm: Add a comment on race window on unload

[tkusumi <tkusumi%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/adcbe02526f8
branches:  trunk
changeset: 465701:adcbe02526f8
user:      tkusumi <tkusumi%NetBSD.org@localhost>
date:      Mon Dec 02 15:17:43 2019 +0000

description:
dm: Add a comment on race window on unload

There is a minor race window on unload vs device creation
that can cause panic.
https://github.com/DragonFlyBSD/DragonFlyBSD/commit/53a07f3ae7313aa58948a60f46428bfc2254dc3c

taken-from: DragonFlyBSD

diffstat:

 sys/dev/dm/device-mapper.c |  3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diffs (17 lines):

diff -r 5a3a7d105388 -r adcbe02526f8 sys/dev/dm/device-mapper.c
--- a/sys/dev/dm/device-mapper.c        Mon Dec 02 14:15:22 2019 +0000
+++ b/sys/dev/dm/device-mapper.c        Mon Dec 02 15:17:43 2019 +0000
@@ -1,4 +1,4 @@
-/*        $NetBSD: device-mapper.c,v 1.40 2018/10/06 14:59:11 mlelstv Exp $ */
+/*        $NetBSD: device-mapper.c,v 1.41 2019/12/02 15:17:43 tkusumi Exp $ */
 
 /*
  * Copyright (c) 2010 The NetBSD Foundation, Inc.
@@ -197,6 +197,7 @@
                 */
                if (dm_dev_counter > 0)
                        return EBUSY;
+               /* race window here */
 
                error = dmdestroy();
                if (error)