[src/trunk]: src/sys/dev/dkwedge dk(4): Prevent race between dkwedge_get_pare...

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

details:   https://anonhg.NetBSD.org/src/rev/80233a23f7b0
branches:  trunk
changeset: 375934:80233a23f7b0
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon May 22 14:59:34 2023 +0000

description:
dk(4): Prevent race between dkwedge_get_parent_name and wedge detach.

Still races with parent detach but maybe this is better.

XXX Maybe we should ditch dkwedge_get_parent_name -- it's used only
by rf_containsboot, which kinda suggests it shouldn't exist.

diffstat:

 sys/dev/dkwedge/dk.c |  21 +++++++++++++++++----
 1 files changed, 17 insertions(+), 4 deletions(-)

diffs (49 lines):

diff -r 081d3a4cf3de -r 80233a23f7b0 sys/dev/dkwedge/dk.c
--- a/sys/dev/dkwedge/dk.c      Mon May 22 14:59:25 2023 +0000
+++ b/sys/dev/dkwedge/dk.c      Mon May 22 14:59:34 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: dk.c,v 1.165 2023/05/22 14:59:25 riastradh Exp $       */
+/*     $NetBSD: dk.c,v 1.166 2023/05/22 14:59:34 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 1.165 2023/05/22 14:59:25 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: dk.c,v 1.166 2023/05/22 14:59:34 riastradh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_dkwedge.h"
@@ -1210,6 +1210,16 @@ dkwedge_lookup(dev_t dev)
        return device_lookup_private(&dk_cd, minor(dev));
 }
 
+static struct dkwedge_softc *
+dkwedge_lookup_acquire(dev_t dev)
+{
+       device_t dv = device_lookup_acquire(&dk_cd, minor(dev));
+
+       if (dv == NULL)
+               return NULL;
+       return device_private(dv);
+}
+
 static int
 dk_open_parent(dev_t dev, int mode, struct vnode **vpp)
 {
@@ -1925,8 +1935,11 @@ dkwedge_get_parent_name(dev_t dev)
 
        if (major(dev) != bmaj && major(dev) != cmaj)
                return NULL;
-       struct dkwedge_softc *sc = dkwedge_lookup(dev);
+
+       struct dkwedge_softc *const sc = dkwedge_lookup_acquire(dev);
        if (sc == NULL)
                return NULL;
-       return sc->sc_parent->dk_name;
+       const char *const name = sc->sc_parent->dk_name;
+       device_release(sc->sc_dev);
+       return name;
 }