kern/94669: Panic from Failed Removable Media Mount

[Jason Harmening]

The following reply was made to PR kern/94669; it has been noted by GNATS.

From: Jason Harmening <jason.harmening at gmail.com>
To: bug-followup at freebsd.org,
 jason.harmening at gmail.com
Cc: Kris Kennaway <kris at obsecurity.org>
Subject: Re: kern/94669: Panic from Failed Removable Media Mount
Date: Sun, 9 Apr 2006 13:55:34 -0500

 The following patch to vfs_mount.c (v1.196.2.8) has worked for me (so far):
 
 --- vfs_mount_old.c     Sat Apr  8 13:47:35 2006
 +++ vfs_mount.c Sun Apr  9 13:46:47 2006
 @@ -924,13 +924,18 @@
                 VI_LOCK(vp);
                 vp->v_iflag &= ~VI_MOUNT;
                 VI_UNLOCK(vp);
 +               error = VFS_ROOT(mp, LK_EXCLUSIVE, &newdp, td);
 +               if (error) {
 +                       VFS_UNMOUNT(mp, 0, td);
 +                       vfs_mount_destroy(mp, td);
 +                       vput(vp);
 +                       return (error);
 +               }
                 vp->v_mountedhere = mp;
                 mtx_lock(&mountlist_mtx);
                 TAILQ_INSERT_TAIL(&mountlist, mp, mnt_list);
                 mtx_unlock(&mountlist_mtx);
                 vfs_event_signal(NULL, VQ_MOUNT, 0);
 -               if (VFS_ROOT(mp, LK_EXCLUSIVE, &newdp, td))
 -                       panic("mount: lost mount");
                 mountcheckdirs(vp, newdp);
                 vput(newdp);
                 VOP_UNLOCK(vp, 0, td);
 
 
 Now if I encounter an I/O error while trying to mount, the mount will simply 
 fail, and I can successfully re-mount with no ill effects.  I've only tested 
 this patch with UFS-formatted media, so I don't know if it will cause 
 problems for other filesystems.  I'm also not very familiar with the FreeBSD 
 vfs, so there could very well be some gaping hole in this patch that I'm not 
 aware of.