vfs: fix d_ancestor() case in d_materialize_unique

In d_materialise_unique() there are 3 subcases to the 'aliased dentry'
case; in two subcases the inode i_lock is properly released but this
does not occur in the -ELOOP subcase.

This seems to have been introduced by commit 1836750115f2 ("fix loop
checks in d_materialise_unique()").

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: stable@vger.kernel.org # v3.0+
[ Added a comment, and moved the unlock to where we generate the -ELOOP,
  which seems to be more natural.

  You probably can't actually trigger this without a buggy network file
  server - d_materialize_unique() is for finding aliases on non-local
  filesystems, and the d_ancestor() case is for a hardlinked directory
  loop.

  But we should be robust in the case of such buggy servers anyway. ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index e9a07b2a0948..b60ddc41d783 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2404,6 +2404,7 @@ struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
                         if (d_ancestor(alias, dentry)) {
                                 /* Check for loops */
                                 actual = ERR_PTR(-ELOOP);
+                                spin_unlock(&inode->i_lock);
                         } else if (IS_ROOT(alias)) {
                                 /* Is this an anonymous mountpoint that we
                                  * could splice into our tree? */
@@ -2413,7 +2414,7 @@ struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
                                 goto found;
                         } else {
                                 /* Nope, but we must(!) avoid directory
-                                 * aliasing */
+                                 * aliasing. This drops inode->i_lock */
                                 actual = __d_unalias(inode, dentry, alias);
                         }
                         write_sequnlock(&rename_lock);