linux-kernel - Re: [PATCH v3 4/4] vfs: Use dlock list for superblock's inode list

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Date:	Tue, 19 Jul 2016 06:23:42 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Waiman Long <Waiman.Long@....com>
Cc:	Jan Kara <jack@...e.com>, Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <dchinner@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH v3 4/4] vfs: Use dlock list for superblock's inode list

On Fri, Jul 15, 2016 at 01:39:43PM -0400, Waiman Long wrote:
>  void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg)
>  {
>  	struct inode *inode, *old_inode = NULL;
> +	DEFINE_DLOCK_LIST_ITER(iter);
>  
> -	spin_lock(&blockdev_superblock->s_inode_list_lock);
> -	list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
> -		struct address_space *mapping = inode->i_mapping;
> +	while (dlock_list_next(&blockdev_superblock->s_inodes, &iter)) {
> +		struct address_space *mapping;
>  
> +		inode   = list_entry(iter.curr, struct inode, i_sb_list);
> +		mapping = inode->i_mapping;

TBH, I would very much prefer something like
	DEFINE_DLOCK_LIST_ITER(iter, &blockdev_superblock->s_inodes);

	dlist_for_each_entry(inode, &iter, i_sb_list) {
		mapping = inode->i_mapping;

> -		spin_unlock(&blockdev_superblock->s_inode_list_lock);
> +		spin_unlock(iter.lock);

... and this might be worth dlist_{un,re}lock(&iter);