f2fs: fix false alarm of lockdep on cp_global_sem lock

f2fs: fix false alarm of lockdep on cp_global_sem lock

lockdep reported a potential deadlock:

a) TCMU device removal context:
 - call del_gendisk() to get q->q_usage_counter
 - call start_flush_work() to get work_completion of wb->dwork
b) f2fs writeback context:
 - in wb_workfn(), which holds work_completion of wb->dwork
 - call f2fs_balance_fs() to get sbi->gc_lock
c) f2fs vfs_write context:
 - call f2fs_gc() to get sbi->gc_lock
 - call f2fs_write_checkpoint() to get sbi->cp_global_sem
d) f2fs mount context:
 - call recover_fsync_data() to get sbi->cp_global_sem
 - call f2fs_check_and_fix_write_pointer() to call blkdev_report_zones()
   that goes down to blk_mq_alloc_request and get q->q_usage_counter

Original callstack is in Closes tag.

However, I think this is a false alarm due to before mount returns
successfully (context d), we can not access file therein via vfs_write
(context c).

Let's introduce per-sb cp_global_sem_key, and assign the key for
cp_global_sem, so that lockdep can recognize cp_global_sem from
different super block correctly.

A lot of work are done by Shin'ichiro Kawasaki, thanks a lot for
the work.

Fixes: c426d99127b1 ("f2fs: Check write pointer consistency of open zones")
Cc: stable@kernel.org
Reported-and-tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Closes: https://lore.kernel.org/linux-f2fs-devel/20260218125237.3340441-1-shinichiro.kawasaki@wdc.com
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>