ext4: fix uninitialized ratelimit_state->lock access in __ext4_fill_super()

In the following concurrency we will access the uninitialized rs->lock:

ext4_fill_super
  ext4_register_sysfs
   // sysfs registered msg_ratelimit_interval_ms
                             // Other processes modify rs->interval to
                             // non-zero via msg_ratelimit_interval_ms
  ext4_orphan_cleanup
    ext4_msg(sb, KERN_INFO, "Errors on filesystem, "
      __ext4_msg
        ___ratelimit(&(EXT4_SB(sb)->s_msg_ratelimit_state)
          if (!rs->interval)  // do nothing if interval is 0
            return 1;
          raw_spin_trylock_irqsave(&rs->lock, flags)
            raw_spin_trylock(lock)
              _raw_spin_trylock
                __raw_spin_trylock
                  spin_acquire(&lock->dep_map, 0, 1, _RET_IP_)
                    lock_acquire
                      __lock_acquire
                        register_lock_class
                          assign_lock_key
                            dump_stack();
  ratelimit_state_init(&sbi->s_msg_ratelimit_state, 5 * HZ, 10);
    raw_spin_lock_init(&rs->lock);
    // init rs->lock here

and get the following dump_stack:

=========================================================
INFO: trying to register non-static key.
The code is fine but needs lockdep annotation, or maybe
you didn't initialize this object before use?
turning off the locking correctness validator.
CPU: 12 PID: 753 Comm: mount Tainted: G E 6.7.0-rc6-next-20231222 #504
[...]
Call Trace:
 dump_stack_lvl+0xc5/0x170
 dump_stack+0x18/0x30
 register_lock_class+0x740/0x7c0
 __lock_acquire+0x69/0x13a0
 lock_acquire+0x120/0x450
 _raw_spin_trylock+0x98/0xd0
 ___ratelimit+0xf6/0x220
 __ext4_msg+0x7f/0x160 [ext4]
 ext4_orphan_cleanup+0x665/0x740 [ext4]
 __ext4_fill_super+0x21ea/0x2b10 [ext4]
 ext4_fill_super+0x14d/0x360 [ext4]
[...]
=========================================================

Normally interval is 0 until s_msg_ratelimit_state is initialized, so
___ratelimit() does nothing. But registering sysfs precedes initializing
rs->lock, so it is possible to change rs->interval to a non-zero value
via the msg_ratelimit_interval_ms interface of sysfs while rs->lock is
uninitialized, and then a call to ext4_msg triggers the problem by
accessing an uninitialized rs->lock. Therefore register sysfs after all
initializations are complete to avoid such problems.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240102133730.1098120-1-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>