Re: kern/41078: mounting ext2fs via vnd causes LOCKDEBUG panic

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

The following reply was made to PR kern/41078; it has been noted by GNATS.

From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: kern-bug-people%NetBSD.org@localhost, gnats-admin%NetBSD.org@localhost, 
netbsd-bugs%NetBSD.org@localhost,
        tsutsui%ceres.dti.ne.jp@localhost
Subject: Re: kern/41078: mounting ext2fs via vnd causes LOCKDEBUG panic
Date: Sat, 12 Sep 2009 02:01:44 +0900

 > >Synopsis:       mounting ext2fs via vnd causes LOCKDEBUG panic
  :
 > panic() at netbsd:panic+0x289
 > lockdebug_abort1() at netbsd:lockdebug_abort1+0xd3
 > rw_exit() at netbsd:rw_exit+0xe9
 > vlockmgr() at netbsd:vlockmgr+0xd8
 > VOP_UNLOCK() at netbsd:VOP_UNLOCK+0x64
 > spec_open() at netbsd:spec_open+0x340
 > VOP_OPEN() at netbsd:VOP_OPEN+0x62
 > ext2fs_mount() at netbsd:ext2fs_mount+0x25a
 > VFS_MOUNT() at netbsd:VFS_MOUNT+0x44
 > do_sys_mount() at netbsd:do_sys_mount+0x62d
 > sys___mount50() at netbsd:sys___mount50+0x33
 > syscall() at netbsd:syscall+0xb6
 
 This is not ext2fs or vnd(4) specific at all.
 
 "mount_ffs /dev/wd7i /mnt" (where no wd7 disk)
 on a LOCKDEBUG kernel is enough to cause this panic.
 
 spec_open() in spec_vnops.c tries to call module_autoload()
 if bdev_open() returns ENXIO (== device not configured),
 but bdev_open() could return ENXIO even if the driver is
 already loaded or builtin. (due to no device, no vnconfig(8) etc.)
 
 The following patch seems to fix the panic and
 vnd.kmod without builtin vnd still works properly,
 but I wonder if it's worth to have some helper functions
 in kern/subr_devsw.c for module_autoload() calls on demand.
 
 ---
 Index: spec_vnops.c
 ===================================================================
 RCS file: /cvsroot/src/sys/miscfs/specfs/spec_vnops.c,v
 retrieving revision 1.124
 diff -u -r1.124 spec_vnops.c
 --- spec_vnops.c       25 Apr 2009 15:06:32 -0000      1.124
 +++ spec_vnops.c       11 Sep 2009 16:28:28 -0000
 @@ -405,11 +405,20 @@
                        vp->v_vflag |= VV_ISTTY;
                VOP_UNLOCK(vp, 0);
                do {
 +                      const struct cdevsw *cdev;
 +
                        gen = module_gen;
                        error = cdev_open(dev, ap->a_mode, S_IFCHR, l);
                        if (error != ENXIO)
                                break;
                        
 +                      /* Check if we already have a valid driver */
 +                      mutex_enter(&device_lock);
 +                      cdev = cdevsw_lookup(dev);
 +                      mutex_exit(&device_lock);
 +                      if (cdev != NULL)
 +                              break;
 +
                        /* Get device name from devsw_conv array */
                        if ((name = cdevsw_getname(major(dev))) == NULL)
                                break;
 @@ -447,11 +456,20 @@
                sd->sd_bdevvp = vp;
                mutex_exit(&device_lock);
                do {
 +                      const struct bdevsw *bdev;
 +
                        gen = module_gen;
                        error = bdev_open(dev, ap->a_mode, S_IFBLK, l);
                        if (error != ENXIO)
                                break;
  
 +                      /* Check if we already have a valid driver */
 +                      mutex_enter(&device_lock);
 +                      bdev = bdevsw_lookup(dev);
 +                      mutex_exit(&device_lock);
 +                      if (bdev != NULL)
 +                              break;
 +
                        /* Get device name from devsw_conv array */
                        if ((name = bdevsw_getname(major(dev))) == NULL)
                                break;
 
 ---
 Izumi Tsutsui