[src/trunk]: src/sys/dev cons(9): Serialize open and close.

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

details:   https://anonhg.NetBSD.org/src/rev/4bf8ea814856
branches:  trunk
changeset: 371716:4bf8ea814856
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Oct 03 19:12:51 2022 +0000

description:
cons(9): Serialize open and close.

Kernel lock wasn't enough for this -- cdevvp, vn_lock, or VOP_OPEN
could block, allowing another thread to re-enter open.

diffstat:

 sys/dev/cons.c |  53 ++++++++++++++++++++++++++++++++++++++++++++---------
 1 files changed, 44 insertions(+), 9 deletions(-)

diffs (119 lines):

diff -r f2e6d45c5a12 -r 4bf8ea814856 sys/dev/cons.c
--- a/sys/dev/cons.c    Mon Oct 03 19:12:29 2022 +0000
+++ b/sys/dev/cons.c    Mon Oct 03 19:12:51 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cons.c,v 1.80 2022/10/03 19:12:29 riastradh Exp $      */
+/*     $NetBSD: cons.c,v 1.81 2022/10/03 19:12:51 riastradh Exp $      */
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -39,7 +39,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: cons.c,v 1.80 2022/10/03 19:12:29 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: cons.c,v 1.81 2022/10/03 19:12:51 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/proc.h>
@@ -53,6 +53,7 @@
 #include <sys/vnode.h>
 #include <sys/kauth.h>
 #include <sys/mutex.h>
+#include <sys/module.h>
 
 #include <dev/cons.h>
 
@@ -83,6 +84,8 @@
        .d_flag = D_TTY
 };
 
+static struct kmutex cn_lock;
+
 struct tty *constty = NULL;    /* virtual console output device */
 struct consdev *cn_tab;        /* physical console device info */
 struct vnode *cn_devvp[2];     /* vnode for underlying device. */
@@ -113,8 +116,12 @@
        if (unit > 1)
                return ENODEV;
 
-       if (cn_tab == NULL)
-               return (0);
+       mutex_enter(&cn_lock);
+
+       if (cn_tab == NULL) {
+               error = 0;
+               goto out;
+       }
 
        /*
         * always open the 'real' console device, so we don't get nailed
@@ -145,15 +152,19 @@
                 */
                panic("cnopen: cn_tab->cn_dev == dev");
        }
-       if (cn_devvp[unit] != NULLVP)
-               return 0;
+       if (cn_devvp[unit] != NULLVP) {
+               error = 0;
+               goto out;
+       }
        if ((error = cdevvp(cndev, &cn_devvp[unit])) != 0) {
                printf("cnopen: unable to get vnode reference\n");
-               return error;
+               goto out;
        }
        vn_lock(cn_devvp[unit], LK_EXCLUSIVE | LK_RETRY);
        error = VOP_OPEN(cn_devvp[unit], flag, kauth_cred_get());
        VOP_UNLOCK(cn_devvp[unit]);
+
+out:   mutex_exit(&cn_lock);
        return error;
 }
 
@@ -165,8 +176,12 @@
 
        unit = minor(dev);
 
-       if (cn_tab == NULL)
-               return (0);
+       mutex_enter(&cn_lock);
+
+       if (cn_tab == NULL) {
+               error = 0;
+               goto out;
+       }
 
        vp = cn_devvp[unit];
        cn_devvp[unit] = NULL;
@@ -174,6 +189,8 @@
        error = VOP_CLOSE(vp, flag, kauth_cred_get());
        VOP_UNLOCK(vp);
        vrele(vp);
+
+out:   mutex_exit(&cn_lock);
        return error;
 }
 
@@ -433,3 +450,21 @@
        *devp = dev;
        return true;
 }
+
+MODULE(MODULE_CLASS_DRIVER, cons, NULL);
+
+static int
+cons_modcmd(modcmd_t cmd, void *arg)
+{
+
+       switch (cmd) {
+       case MODULE_CMD_INIT:
+               mutex_init(&cn_lock, MUTEX_DEFAULT, IPL_NONE);
+               return 0;
+       case MODULE_CMD_FINI:
+               mutex_destroy(&cn_lock);
+               return 0;
+       default:
+               return ENOTTY;
+       }
+}