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SubjectRe: WARNING in lock_release
On Thu, Nov 16, 2017 at 02:56:00AM -0800, syzbot wrote:
> Hello,
>
> syzkaller hit the following crash on
> 5515cf16e270538121e4fa9283fed86c6cfd8c9c
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers

Hmm... That's alloc_super() buggering off on allocation failure and
hitting up_write(s->s_umount) in destroy_unused_super(), since it has
not done
init_rwsem(&s->s_umount);
lockdep_set_class(&s->s_umount, &type->s_umount_key);
down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
part yet. The sucker is just all-zeroes here. The easiest way to fix
that would probably be to move that bit of initialization in the very
beginning...

diff --git a/fs/super.c b/fs/super.c
index 8ca15415351a..2808aeaf5337 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -190,6 +190,24 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,

INIT_LIST_HEAD(&s->s_mounts);
s->s_user_ns = get_user_ns(user_ns);
+ init_rwsem(&s->s_umount);
+ lockdep_set_class(&s->s_umount, &type->s_umount_key);
+ /*
+ * 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);

if (security_sb_alloc(s))
goto fail;
@@ -217,25 +235,6 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
goto fail;
if (list_lru_init_memcg(&s->s_inode_lru))
goto fail;
-
- init_rwsem(&s->s_umount);
- lockdep_set_class(&s->s_umount, &type->s_umount_key);
- /*
- * 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 = 1;
atomic_set(&s->s_active, 1);
mutex_init(&s->s_vfs_rename_mutex);
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