Re: [PATCH] blk-throttle: check policy bit in blk_throtl_activated()

[Han Guangjiang <gj.han@foxmail.com>]

Hi,

> Yes, however, this can be fixed very similar:
> 
> Set sq->parent_sq to NULL here, and add a helper parent_sq(q, sq):
> 
> if (sq->parent_sq)
>         return sq->parent_sq;
> 
> td_sq = &q->td->service_queue;
> return sq == td_sq ? NULL : td_sq;
> 
> And sq_to_tg() need to be changed as well. So far, I'm not sure how many
> code changes are required this way. We of course want a simple fix for
> stable backport, but we definitely still want this kind of fix in future
> release.

We preliminarily tried implementing this approach. But the changes are 
scattered and backport might be complex. So we provide a simple fix first.

> Meanwhile, please remove the comment about freeze queue, turns out it
> can't protect blk_throtl_bio() becasue q_usage_coutner is not grabbed
> yet while issuing bio.

As discussed before, we also removed some outdated comments in 
blk_should_throtl().

We just submitted v2 which includes the changes.

We look forward to your feedback and suggestions on the v2 patch.

Thanks,
Han Guangjiang