Re: [f2fs-dev] [PATCH v2 1/1] f2fs: fix lockdep WARN of sbi->cp_global_sem and q->q_usage_counter

[Jaegeuk Kim via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 02/24, Shinichiro Kawasaki wrote:
> On Feb 24, 2026 / 03:26, Jaegeuk Kim wrote:
> > On 02/18, Shin'ichiro Kawasaki wrote:
> > > From: Shin'ichiro Kawasaki via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>
> > > 
> > > 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")
> > > Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> > > Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> > > ---
> > >  fs/f2fs/recovery.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
> > > index a26071f2b0bc..87fd6cd436fe 100644
> > > --- a/fs/f2fs/recovery.c
> > > +++ b/fs/f2fs/recovery.c
> > > @@ -922,6 +922,8 @@ int f2fs_recover_fsync_data(struct f2fs_sb_info *sbi, bool check_only)
> > >  		truncate_inode_pages_final(META_MAPPING(sbi));
> > >  	}
> > >  
> > > +	f2fs_up_write_trace(&sbi->cp_global_sem, &lc);
> > > +
> > >  	/*
> > >  	 * If fsync data succeeds or there is no fsync data to recover,
> > >  	 * and the f2fs is not read only, check and fix zoned block devices'
> > > @@ -933,8 +935,6 @@ int f2fs_recover_fsync_data(struct f2fs_sb_info *sbi, bool check_only)
> > >  	if (!err)
> > >  		clear_sbi_flag(sbi, SBI_POR_DOING);
> > >  
> > > -	f2fs_up_write_trace(&sbi->cp_global_sem, &lc);
> > > -
> > 
> > This was a guard to prevent checkpoint during f2fs_check_and_fix_write_pointer()
> > where it changes the checkpoint as well?
> 
> I checked f2fs_check_and_fix_write_pointer() again, and it does not look
> changing the checkpoint to me. FYI, here I show the rough function call chain
> from f2fs_check_and_fix_write_pointer() as below. I guess this call chain does
> not change the checkpoint, but if I misunderstand anything, please let me know.
> 
>  f2fs_check_and_fix_write_pointer()
>   fix_curseg_write_pointer()
>    do_fix_curseg_write_pointer()
>     blkdev_report_zones()
>      report_one_zone_cb()
>     f2fs_allocate_new_section()
>      __allocate_new_segment()
>       new_curseg()

E.g., curseg.

>       locate_dirty_segment()
>        __locate_dirty_segment()
>        __remove_dirty_segment()
>     check_zone_write_pointer()
>      __f2fs_issue_discard_zone()
>      blkdev_zone_mgmt()
>      blkdev_issue_zeroout()
>     __f2fs_issue_discard_zone()
>   check_write_pointer(sbi)
>    blkdev_report_zones()
>     check_zone_writer_pointer_cb()
>      check_zone_write_pointer()
>       __f2fs_issue_discard_zone()
>       blkdev_zone_mgmt()
>       blkdev_issue_zeroout()
> 
> > 
> > >  	/* let's drop all the directory inodes for clean checkpoint */
> > >  	destroy_fsync_dnodes(&dir_list, err);
> > >  
> > > -- 
> > > 2.49.0


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