[src/trunk]: src/sys/dev/dkwedge dk(4): Serialize closing parent's dk_rawvp w...

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

details:   https://anonhg.NetBSD.org/src/rev/e0c4183c2754
branches:  trunk
changeset: 369567:e0c4183c2754
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Aug 22 00:19:12 2022 +0000

description:
dk(4): Serialize closing parent's dk_rawvp with opening it.

Otherwise, the following events might happen:

- process 123 had /dev/rdkN open, starts close, enters dk_close_parent
- process 456 opens /dev/rdkM (same parent, different wedge), calls
  dk_open_parent

At this point, the block device hasn't yet closed, so dk_open_parent
will fail with EBUSY.  This is incorrect -- the chardev is never
supposed to fail with EBUSY, and dkopen/dkclose carefully manage
state to avoid opening the block device while it's still open.  The
problem is that dkopen in process 456 didn't wait for vn_close
in process 123 to finish before calling VOP_OPEN.

(Note: If it were the _same_ chardev /dev/rdkN in both processes,
then spec_open/close would prevent this.  But since it's a
_different_ chardev, spec_open/close assume that concurrency is OK,
and it's the driver's responsibility to serialize access to the
parent disk which, unbeknownst to spec_open/close, is shared between
dkN and dkM.)

It appears that the vn_close call was previously moved outside
dk_rawlock in 2010 to work around an unrelated bug in raidframe that
had already been fixed in HEAD:

Crash pointing to dk_rawlock and raidclose:
https://mail-index.netbsd.org/tech-kern/2010/07/27/msg008612.html

Change working around that crash:
https://mail-index.netbsd.org/source-changes/2010/08/04/msg012270.html

Change removing raidclose -> mutex_destroy(&dk_rawlock) path:
https://mail-index.netbsd.org/source-changes/2009/07/23/msg223381.html

diffstat:

 sys/dev/dkwedge/dk.c |  10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diffs (35 lines):

diff -r 3db9db5769d2 -r e0c4183c2754 sys/dev/dkwedge/dk.c
--- a/sys/dev/dkwedge/dk.c      Sun Aug 21 22:28:26 2022 +0000
+++ b/sys/dev/dkwedge/dk.c      Mon Aug 22 00:19:12 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: dk.c,v 1.112 2022/06/11 18:17:00 martin Exp $  */
+/*     $NetBSD: dk.c,v 1.113 2022/08/22 00:19:12 riastradh Exp $       */
 
 /*-
  * Copyright (c) 2004, 2005, 2006, 2007 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: dk.c,v 1.112 2022/06/11 18:17:00 martin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: dk.c,v 1.113 2022/08/22 00:19:12 riastradh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_dkwedge.h"
@@ -1220,13 +1220,13 @@
                }
        }
 
-       mutex_exit(&sc->sc_parent->dk_rawlock);
-       mutex_exit(&sc->sc_dk.dk_openlock);
-
        if (vp) {
                dk_close_parent(vp, mode);
        }
 
+       mutex_exit(&sc->sc_parent->dk_rawlock);
+       mutex_exit(&sc->sc_dk.dk_openlock);
+
        return error;
 }