On Tue, Feb 22, 2022 at 09:27:23AM +0100, Jan Kara wrote:

On Thu 17-02-22 20:10:03, Byungchul Park wrote:

quoted

[    7.009608] ===================================================
[    7.009613] DEPT: Circular dependency has been detected.
[    7.009614] 5.17.0-rc1-00014-g8a599299c0cb-dirty #30 Tainted: G        W
[    7.009616] ---------------------------------------------------
[    7.009617] summary
[    7.009618] ---------------------------------------------------
[    7.009618] *** DEADLOCK ***
[    7.009618]
[    7.009619] context A
[    7.009619]     [S] (unknown)(&(bit_wait_table + i)->dmap:0)
[    7.009621]     [W] down_write(&ei->i_data_sem:0)
[    7.009623]     [E] event(&(bit_wait_table + i)->dmap:0)
[    7.009624]
[    7.009625] context B
[    7.009625]     [S] down_read(&ei->i_data_sem:0)
[    7.009626]     [W] wait(&(bit_wait_table + i)->dmap:0)
[    7.009627]     [E] up_read(&ei->i_data_sem:0)
[    7.009628]

Looking into this I have noticed that Dept here tracks bitlocks (buffer
locks in particular) but it apparently treats locks on all buffers as one
locking class so it conflates lock on superblock buffer with a lock on
extent tree block buffer. These are wastly different locks with different
locking constraints. So to avoid false positives in filesystems we will
need to add annotations to differentiate locks on different buffers (based
on what the block is used for). Similarly how we e.g. annotate i_rwsem for
different inodes.

Hi Jan Kara,

I just understood why some guys in this space got mad at Dept reports.
I barely got reports from the lock you mentioned with my system -
precisely speaking only one, even though I've been rebooting my system
many times. But another report that someone gave for me showed there
were a lot of reports from the lock.

Your comment and the report are so much helpful. I need to assign
each's own class first for the buffer locks. Thank you very much.

Thanks,
Byungchul

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR