Re: [PATCH v3 2/2] writeback: Fix false warning in inode_to_wb()

[Andrew Morton]

On Sat, 12 Apr 2025 18:39:12 +0200 Andreas Gruenbacher <agruenba@xxxxxxxxxx> wrote:

> From: Jan Kara <jack@xxxxxxx>
> 
> inode_to_wb() is used also for filesystems that don't support cgroup
> writeback. For these filesystems inode->i_wb is stable during the
> lifetime of the inode (it points to bdi->wb) and there's no need to hold
> locks protecting the inode->i_wb dereference. Improve the warning in
> inode_to_wb() to not trigger for these filesystems.
> 
> ...
>
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -249,6 +249,7 @@ static inline struct bdi_writeback *inode_to_wb(const struct inode *inode)
>  {
>  #ifdef CONFIG_LOCKDEP
>  	WARN_ON_ONCE(debug_locks &&
> +		     (inode->i_sb->s_iflags & SB_I_CGROUPWB) &&
>  		     (!lockdep_is_held(&inode->i_lock) &&
>  		      !lockdep_is_held(&inode->i_mapping->i_pages.xa_lock) &&
>  		      !lockdep_is_held(&inode->i_wb->list_lock)));

Is this a does-nothing now GFS2 has been altered?

Otherwise, a bogus WARN is something we'll want to eliminate from
-stable kernels also.  Are we able to identify a Fixes: for this?

Thanks.