[PATCH] f2fs: fix false alarm of lockdep on cp_global_sem lock

Chao Yu
2026-03-06T12:24:35Z

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>
---
fs/f2fs/f2fs.h | 3 +++
fs/f2fs/super.c | 11 +++++++++++
2 files changed, 14 insertions(+)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 8942b2a63cfd..87a83c21837c 100644
--- a/fs/f2fs/f2fs.h
+++ b/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 */
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 8774c60b4be4..1d97dded4ee5 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4948,6 +4948,11 @@ 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);
@@ -5419,6 +5424,9 @@ 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;

@@ -5500,6 +5508,9 @@ 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;
}
--
2.49.0