Add a BUG_ON() to check for passing an unreferenced dentry to dput().

This is analogous to the similar check in dget(), and will make
reference-counting bugs in filesystems more immediately obvious. (I
just spent a while debugging an oops that turned out to be due to
broken fs reference counting.)

Signed-off-by: Paul Menage <menage@google.com>

---
 fs/dcache.c |    1 +
 1 file changed, 1 insertion(+)

Index: container-2.6.23-rc3-mm1/fs/dcache.c
===================================================================
--- container-2.6.23-rc3-mm1.orig/fs/dcache.c
+++ container-2.6.23-rc3-mm1/fs/dcache.c
@@ -176,6 +176,7 @@ void dput(struct dentry *dentry)
 	if (!dentry)
 		return;
 
+	BUG_ON(!atomic_read(&dentry->d_count));
 repeat:
 	if (atomic_read(&dentry->d_count) == 1)
 		might_sleep();
-
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