[dm-devel] [PATCH v2 2/2] blk-throttle: fix wrong initialization in case of dm device

[Mike Snitzer]

On Sun, Nov 19, 2017 at 9:00 PM, Joseph Qi <jiangqi903 at gmail.com> wrote:
> From: Joseph Qi <qijiang.qj at alibaba-inc.com>
>
> dm device set QUEUE_FLAG_NONROT in resume, which is after register
> queue. That is to mean, the previous initialization in
> blk_throtl_register_queue is wrong in this case.
> Fix it by checking and then updating the info during root tg
> initialization as we don't have a better choice.

Given DM motivated this change, curious why you didn't send this to dm-devel?

In any case, not sure why you need to reference "resume".  Very few
people will appreciate that detail.

Better to just say: DM device sets QUEUE_FLAG_NONROT after the queue
is registered.

> Signed-off-by: Joseph Qi <qijiang.qj at alibaba-inc.com>
> ---
>  block/blk-throttle.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index bf52035..6d6b220 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -541,6 +541,23 @@ static void throtl_pd_init(struct blkg_policy_data *pd)
>         if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
>                 sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
>         tg->td = td;
> +
> +       /*
> +        * dm device set QUEUE_FLAG_NONROT in resume, which is after resister
> +        * queue, so the previous initialization is wrong in this case. Check
> +        * and update it here.
> +        */

typo: s/resister/register/
But again, best to say:
DM device sets QUEUE_FLAG_NONROT after the queue is registered, ...

Also, an alternative to your patch would be to have DM's
dm_table_set_restrictions() call a blk-throttle function to setup
blk-throttle after it is done setting queue flags?
Saves all other drivers from having to run this 2 stage initialization
code.. just a thought.

Mike