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

[Al Viro]

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);