linux-kernel - Re: [PATCH v7 1/6] writeback, cgroup: do not switch inodes with I_WILL

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Date:   Mon, 7 Jun 2021 10:48:31 +0200
From:   Jan Kara <jack@...e.cz>
To:     Roman Gushchin <guro@...com>
Cc:     Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Dennis Zhou <dennis@...nel.org>,
        Dave Chinner <dchinner@...hat.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH v7 1/6] writeback, cgroup: do not switch inodes with
 I_WILL_FREE flag

On Thu 03-06-21 18:31:54, Roman Gushchin wrote:
> If an inode's state has I_WILL_FREE flag set, the inode will be
> freed soon, so there is no point in trying to switch the inode
> to a different cgwb.
> 
> I_WILL_FREE was ignored since the introduction of the inode switching,
> so it looks like it doesn't lead to any noticeable issues for a user.
> This is why the patch is not intended for a stable backport.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Roman Gushchin <guro@...com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/fs-writeback.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index e91980f49388..bd99890599e0 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -389,10 +389,10 @@ static void inode_switch_wbs_work_fn(struct work_struct *work)
>  	xa_lock_irq(&mapping->i_pages);
>  
>  	/*
> -	 * Once I_FREEING is visible under i_lock, the eviction path owns
> -	 * the inode and we shouldn't modify ->i_io_list.
> +	 * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
> +	 * path owns the inode and we shouldn't modify ->i_io_list.
>  	 */
> -	if (unlikely(inode->i_state & I_FREEING))
> +	if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
>  		goto skip_switch;
>  
>  	trace_inode_switch_wbs(inode, old_wb, new_wb);
> @@ -517,7 +517,7 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id)
>  	/* while holding I_WB_SWITCH, no one else can update the association */
>  	spin_lock(&inode->i_lock);
>  	if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
> -	    inode->i_state & (I_WB_SWITCH | I_FREEING) ||
> +	    inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
>  	    inode_to_wb(inode) == isw->new_wb) {
>  		spin_unlock(&inode->i_lock);
>  		goto out_free;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR