From: Miklos Szeredi <miklos@szeredi.hu>
This patch fixes a problem when a inode which is the root of a mount
becomes bad (make_bad_inode()). In this case follow_link will return
-EIO, so the name resolution fails, and umount won't work. The
solution is just to remove the follow_link method from bad_inode_ops.
Any filesystem operation (other than unmount) will still fail, since
every other method returns -EIO.
A test case for this is:
1) export an smbfs on host A and mount the share on host B
2) create directory X on A under the exported directory
3) bind mount X to Y on B (Y need not be under the share)
4) remove directory X, and create regular file X (same name) on A
5) stat X on B, this will make X a bad inode (file type changed)
6) umount Y
Without the patch applied, umount won't succeed, and a reboot is
necessary to get rid of the mount.
With the patch applied, umount will succeed.
The same is true for any filesystem which uses make_bad_inode() to
mark an existing inode bad (NFS, SMBFS, FUSE, etc...).
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/fs/bad_inode.c | 14 ++------------
1 files changed, 2 insertions(+), 12 deletions(-)
diff -puN fs/bad_inode.c~cant-unmount-bad-inode fs/bad_inode.c
--- 25/fs/bad_inode.c~cant-unmount-bad-inode Mon Jan 24 14:06:32 2005
+++ 25-akpm/fs/bad_inode.c Mon Jan 24 14:06:32 2005
@@ -15,17 +15,6 @@
#include <linux/smp_lock.h>
#include <linux/namei.h>
-/*
- * The follow_link operation is special: it must behave as a no-op
- * so that a bad root inode can at least be unmounted. To do this
- * we must dput() the base and return the dentry with a dget().
- */
-static int bad_follow_link(struct dentry *dent, struct nameidata *nd)
-{
- nd_set_link(nd, ERR_PTR(-EIO));
- return 0;
-}
-
static int return_EIO(void)
{
return -EIO;
@@ -70,7 +59,8 @@ struct inode_operations bad_inode_ops =
.mknod = EIO_ERROR,
.rename = EIO_ERROR,
.readlink = EIO_ERROR,
- .follow_link = bad_follow_link,
+ /* follow_link must be no-op, otherwise unmounting this inode
+ won't work */
.truncate = EIO_ERROR,
.permission = EIO_ERROR,
.getattr = EIO_ERROR,
_