1 files changed, 16 insertions, 1 deletions

diff --git a/fs/super.c b/fs/super.c
index 61dce001dd57..8349ed6b1412 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -82,7 +82,22 @@ static struct super_block *alloc_super(struct file_system_type *type)
                  * lock ordering than usbfs:
                  */
                 lockdep_set_class(&s->s_lock, &type->s_lock_key);
-                down_write(&s->s_umount);
+                /*
+                 * sget() can have s_umount recursion.
+                 *
+                 * When it cannot find a suitable sb, it allocates a new
+                 * one (this one), and tries again to find a suitable old
+                 * one.
+                 *
+                 * In case that succeeds, it will acquire the s_umount
+                 * lock of the old one. Since these are clearly distrinct
+                 * locks, and this object isn't exposed yet, there's no
+                 * risk of deadlocks.
+                 *
+                 * Annotate this by putting this lock in a different
+                 * subclass.
+                 */
+                down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
                 s->s_count = S_BIAS;
                 atomic_set(&s->s_active, 1);
                 mutex_init(&s->s_vfs_rename_mutex);