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: c426d99 ("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>

Author: chaseyu

fs/f2fs/f2fs.h

@@ -2042,6 +2042,9 @@ struct f2fs_sb_info {
 	spinlock_t iostat_lat_lock;
 	struct iostat_lat_info *iostat_io_lat;
 #endif
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lock_class_key cp_global_sem_key;
+#endif
 };
 
 /* Definitions to access f2fs_sb_info */

fs/f2fs/super.c

@@ -4964,6 +4964,11 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
 	init_f2fs_rwsem_trace(&sbi->gc_lock, sbi, LOCK_NAME_GC_LOCK);
 	mutex_init(&sbi->writepages);
 	init_f2fs_rwsem_trace(&sbi->cp_global_sem, sbi, LOCK_NAME_CP_GLOBAL);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	lockdep_register_key(&sbi->cp_global_sem_key);
+	lockdep_set_class(&sbi->cp_global_sem.internal_rwsem,
+					&sbi->cp_global_sem_key);
+#endif
 	init_f2fs_rwsem_trace(&sbi->node_write, sbi, LOCK_NAME_NODE_WRITE);
 	init_f2fs_rwsem_trace(&sbi->node_change, sbi, LOCK_NAME_NODE_CHANGE);
 	spin_lock_init(&sbi->stat_lock);
@@ -5435,6 +5440,9 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
 free_sb_buf:
 	kfree(raw_super);
 free_sbi:
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	lockdep_unregister_key(&sbi->cp_global_sem_key);
+#endif
 	kfree(sbi);
 	sb->s_fs_info = NULL;
 
@@ -5516,6 +5524,9 @@ static void kill_f2fs_super(struct super_block *sb)
 	/* Release block devices last, after fscrypt_destroy_keyring(). */
 	if (sbi) {
 		destroy_device_list(sbi);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+		lockdep_unregister_key(&sbi->cp_global_sem_key);
+#endif
 		kfree(sbi);
 		sb->s_fs_info = NULL;
 	}