1 files changed, 20 insertions, 2 deletions

diff --git a/fs/super.c b/fs/super.c
index 61dce001dd57..6ce501447ada 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);
@@ -356,8 +371,10 @@ retry:
                                 continue;
                         if (!grab_super(old))
                                 goto retry;
-                        if (s)
+                        if (s) {
+                                up_write(&s->s_umount);
                                 destroy_super(s);
+                        }
                         return old;
                 }
         }
@@ -372,6 +389,7 @@ retry:
         err = set(s, data);
         if (err) {
                 spin_unlock(&sb_lock);
+                up_write(&s->s_umount);
                 destroy_super(s);
                 return ERR_PTR(err);
         }