[PATCH] don't invalidate non-directory mountpoints

[Miklos Szeredi <miklos@szeredi.hu>]

d_invalidate allowed a non-directory mountpoint to be invalidated,
which is bad, since the mountpoint becomes unreachable.

I know it's racy wrt attaching/detaching mount, but AFAICS so is
everything else that unhashes the dentry.  This seems to be an
oversight when splitting out vfsmount_lock from dcache_lock.  To be
fixed.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
---

Index: linux/fs/dcache.c
===================================================================
--- linux.orig/fs/dcache.c	2005-10-04 13:59:57.000000000 +0200
+++ linux/fs/dcache.c	2005-10-07 12:59:11.000000000 +0200
@@ -350,7 +350,8 @@ int d_invalidate(struct dentry * dentry)
 	 */
 	spin_lock(&dentry->d_lock);
 	if (atomic_read(&dentry->d_count) > 1) {
-		if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
+		if (dentry->d_inode && (S_ISDIR(dentry->d_inode->i_mode) ||
+					d_mountpoint(dentry))) {
 			spin_unlock(&dentry->d_lock);
 			spin_unlock(&dcache_lock);
 			return -EBUSY;
-
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