nfs d_revalidate() is too trigger-happy with d_drop()

If dentry found stale happens to be a root of disconnected tree, we
can't d_drop() it; its d_hash is actually part of s_anon and d_drop()
would simply hide it from shrink_dcache_for_umount(), leading to
all sorts of fun, including busy inodes on umount and oopsen after
that.

Bug had been there since at least 2006 (commit c636eb already has it),
so it's definitely -stable fodder.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index be46f26c9a5616cc2181fa98b9d9b7157a2cd7ce..db3ad849a289fe88e0286fe873d6369ca085a34b 100644 (file)
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -837,6 +837,8 @@ out_zap_parent:
                /* If we have submounts, don't unhash ! */
                if (have_submounts(dentry))
                        goto out_valid;
+               if (dentry->d_flags & DCACHE_DISCONNECTED)
+                       goto out_valid;
                shrink_dcache_parent(dentry);
        }
        d_drop(dentry);