linux-kernel - Re: [PATCH v3 2/2] writeback: Fix false warning in inode_to

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Message-ID: <6k6kbrcw5bythxn7xu2u7xm4ssaiprnzr42qmf2oqyd6igdoy7@cyv67iatitvq>
Date: Mon, 14 Apr 2025 15:55:37 +0200
From: Jan Kara <jack@...e.cz>
To: Andreas Gruenbacher <agruenba@...hat.com>
Cc: cgroups@...r.kernel.org, Jan Kara <jack@...e.cz>, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Rafael Aquini <aquini@...hat.com>, gfs2@...ts.linux.dev, 
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 2/2] writeback: Fix false warning in inode_to_wb()

Hi Andrew!

Can you please take this patch through MM tree? Thanks! Andreas is already
taking the first patch in the series through GFS2 tree.

								Honza

On Sat 12-04-25 18:39:12, Andreas Gruenbacher wrote:
> From: Jan Kara <jack@...e.cz>
> 
> 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.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>
> Reviewed-by: Andreas Gruenbacher <agruenba@...hat.com>
> ---
>  include/linux/backing-dev.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 8e7af9a03b41..e721148c95d0 100644
> --- 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)));
> -- 
> 2.48.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR