Re: dm: fix congested_fn for request-based device

[Mike Snitzer <snitzer@redhat.com>]

On Tue, Mar 03 2020 at  3:45am -0500,
Hou Tao <houtao1@huawei.com> wrote:

> We neither assign congested_fn for requested-based blk-mq device
> nor implement it correctly. So fix both.
> 
> Fixes: 4aa9c692e052 ("bdi: separate out congested state into a separate struct")
> Signed-off-by: Hou Tao <houtao1@huawei.com>
> ---
>  drivers/md/dm.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index b89f07ee2eff..80b95e21db43 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1784,11 +1784,13 @@ static int dm_any_congested(void *congested_data, int bdi_bits)
>  
>  	if (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
>  		if (dm_request_based(md)) {
> +			struct backing_dev_info *bdi =
> +				md->queue->backing_dev_info;
>  			/*
>  			 * With request-based DM we only need to check the
>  			 * top-level queue for congestion.
>  			 */
> -			r = md->queue->backing_dev_info->wb.state & bdi_bits;
> +			r = bdi->wb.congested->state & bdi_bits;
>  		} else {
>  			map = dm_get_live_table_fast(md);
>  			if (map)

The above change does indeed fix missing conversion that should've
occurred in commit 4aa9c692e052.

> @@ -2265,6 +2267,7 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
>  			DMERR("Cannot initialize queue for request-based dm-mq mapped device");
>  			return r;
>  		}
> +		dm_init_normal_md_queue(md);
>  		break;
>  	case DM_TYPE_BIO_BASED:
>  	case DM_TYPE_DAX_BIO_BASED:

I've renamed dm_init_normal_md_queue to dm_init_congested_fn and removed
it's incorrect comment.

Here is the final fix I just staged:
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-5.6&id=974f51e8633f0f3f33e8f86bbb5ae66758aa63c7

Thanks,
Mike