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Date: Tue, 19 Jul 2016 06:23:42 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Waiman Long <Waiman.Long@hpe.com>
Cc: Jan Kara <jack@suse.com>, Jeff Layton <jlayton@poochiereds.net>,
        "J. Bruce Fields" <bfields@fieldses.org>, Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Andi Kleen <andi@firstfloor.org>, Dave Chinner <dchinner@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [PATCH v3 4/4] vfs: Use dlock list for superblock's inode list
Message-ID: <20160719052342.GF2356@ZenIV.linux.org.uk>
References: <1468604383-40362-1-git-send-email-Waiman.Long@hpe.com>
 <1468604383-40362-5-git-send-email-Waiman.Long@hpe.com>
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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);