1 files changed, 44 insertions, 7 deletions

diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c
index b8ac7b7faf61..e3ea6fe7edb4 100644
--- a/fs/smb/client/cached_dir.c
+++ b/fs/smb/client/cached_dir.c
@@ -16,6 +16,7 @@ static struct cached_fid *init_cached_dir(const char *path);
 static void free_cached_dir(struct cached_fid *cfid);
 static void smb2_close_cached_fid(struct kref *ref);
 static void cfids_laundromat_worker(struct work_struct *work);
+static void close_cached_dir_locked(struct cached_fid *cfid);
 
 struct cached_dir_dentry {
 	struct list_head entry;
@@ -388,11 +389,11 @@ out:
 			 * lease. Release one here, and the second below.
 			 */
 			cfid->has_lease = false;
-			kref_put(&cfid->refcount, smb2_close_cached_fid);
+			close_cached_dir_locked(cfid);
 		}
 		spin_unlock(&cfids->cfid_list_lock);
 
-		kref_put(&cfid->refcount, smb2_close_cached_fid);
+		close_cached_dir(cfid);
 	} else {
 		*ret_cfid = cfid;
 		atomic_inc(&tcon->num_remote_opens);
@@ -438,12 +439,14 @@ int open_cached_dir_by_dentry(struct cifs_tcon *tcon,
 
 static void
 smb2_close_cached_fid(struct kref *ref)
+__releases(&cfid->cfids->cfid_list_lock)
 {
 	struct cached_fid *cfid = container_of(ref, struct cached_fid,
 					       refcount);
 	int rc;
 
-	spin_lock(&cfid->cfids->cfid_list_lock);
+	lockdep_assert_held(&cfid->cfids->cfid_list_lock);
+
 	if (cfid->on_list) {
 		list_del(&cfid->entry);
 		cfid->on_list = false;
@@ -478,15 +481,49 @@ void drop_cached_dir_by_name(const unsigned int xid, struct cifs_tcon *tcon,
 	spin_lock(&cfid->cfids->cfid_list_lock);
 	if (cfid->has_lease) {
 		cfid->has_lease = false;
-		kref_put(&cfid->refcount, smb2_close_cached_fid);
+		close_cached_dir_locked(cfid);
 	}
 	spin_unlock(&cfid->cfids->cfid_list_lock);
 	close_cached_dir(cfid);
 }
 
-
+/**
+ * close_cached_dir - drop a reference of a cached dir
+ *
+ * The release function will be called with cfid_list_lock held to remove the
+ * cached dirs from the list before any other thread can take another @cfid
+ * ref. Must not be called with cfid_list_lock held; use
+ * close_cached_dir_locked() called instead.
+ *
+ * @cfid: cached dir
+ */
 void close_cached_dir(struct cached_fid *cfid)
 {
+	lockdep_assert_not_held(&cfid->cfids->cfid_list_lock);
+	kref_put_lock(&cfid->refcount, smb2_close_cached_fid, &cfid->cfids->cfid_list_lock);
+}
+
+/**
+ * close_cached_dir_locked - put a reference of a cached dir with
+ * cfid_list_lock held
+ *
+ * Calling close_cached_dir() with cfid_list_lock held has the potential effect
+ * of causing a deadlock if the invariant of refcount >= 2 is false.
+ *
+ * This function is used in paths that hold cfid_list_lock and expect at least
+ * two references. If that invariant is violated, WARNs and returns without
+ * dropping a reference; the final put must still go through
+ * close_cached_dir().
+ *
+ * @cfid: cached dir
+ */
+static void close_cached_dir_locked(struct cached_fid *cfid)
+{
+	lockdep_assert_held(&cfid->cfids->cfid_list_lock);
+
+	if (WARN_ON(kref_read(&cfid->refcount) < 2))
+		return;
+
 	kref_put(&cfid->refcount, smb2_close_cached_fid);
 }
 
@@ -596,7 +633,7 @@ cached_dir_offload_close(struct work_struct *work)
 
 	WARN_ON(cfid->on_list);
 
-	kref_put(&cfid->refcount, smb2_close_cached_fid);
+	close_cached_dir(cfid);
 	cifs_put_tcon(tcon, netfs_trace_tcon_ref_put_cached_close);
 }
 
@@ -762,7 +799,7 @@ static void cfids_laundromat_worker(struct work_struct *work)
 			 * Drop the ref-count from above, either the lease-ref (if there
 			 * was one) or the extra one acquired.
 			 */
-			kref_put(&cfid->refcount, smb2_close_cached_fid);
+			close_cached_dir(cfid);
 	}
 	queue_delayed_work(cfid_put_wq, &cfids->laundromat_work,
 			   dir_cache_timeout * HZ);