On 2/1/26 21:22, Shin'ichiro Kawasaki wrote:
> A lockdep WARN is observed recently under the following steps:
>
> 1) Create a zoned TCMU device
> 2) Create a f2fs filesystem on the zoned TCMU device and mount it
> 3) Fill the filesystem with files and trigger GC
> 4) Unmout the filesystem
> 5) Remove the zoned TCMU device
>
> The lockdep WARN indicates that a circular lock depedency formed by four
> contexts, as described below.
>
> 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
>
> To suppress the WARN, cut the dependency d) between sbi->cp_global_sem
> and q->q_usage_counter. For that purpose, move the
> f2fs_check_and_fix_write_pointer() call outside of the critical section
> of sbi->cp_global_sem in f2fs_recovery_fsync_data(). This change is fine
> because the write pointer fix operation only affects the main segments
> and does not interact with the check point metadata. Furthermore,
> conflicts between the write pointer fix operation and data/node flush
> operations remain protected by SBI_POR_DOING.
>
> Fixes: c426d99127b1 ("f2fs: Check write pointer consistency of open zones")
> Signed-off-by: Shin'ichiro Kawasaki <[email protected]>
Looks OK to me.
Reviewed-by: Damien Le Moal <[email protected]>
--
Damien Le Moal
Western Digital Research
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