linux-kernel - Re: [PATCH] blk-throttle: check policy bit in blk_throtl

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Message-ID: <tencent_329AB29889A28A31719F322691C87E214C07@qq.com>
Date: Thu,  4 Sep 2025 16:19:37 +0800
From: Han Guangjiang <gj.han@...mail.com>
To: yukuai1@...weicloud.com
Cc: axboe@...nel.dk,
	fanggeng@...iang.com,
	gj.han@...mail.com,
	hanguangjiang@...iang.com,
	liangjie@...iang.com,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yangchen11@...iang.com
Subject: Re: [PATCH] blk-throttle: check policy bit in blk_throtl_activated()

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As discussed before, we also removed some outdated comments in 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