linux-kernel - Re: [PATCH] block: cancel all throttled bios when deleting the cgroup

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Date: Fri, 28 Jun 2024 10:04:58 +0800
From: Li Lingfeng <lilingfeng@...weicloud.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: tj@...nel.org, josef@...icpanda.com, hch@....de, axboe@...nel.dk,
 cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yangerkun@...wei.com, yukuai1@...weicloud.com,
 houtao1@...wei.com, yi.zhang@...wei.com, lilingfeng3@...wei.com
Subject: Re: [PATCH] block: cancel all throttled bios when deleting the cgroup


在 2024/6/27 22:48, Michal Koutný 写道:
> On Tue, Jun 25, 2024 at 07:38:34PM GMT, Li Lingfeng <lilingfeng@...weicloud.com> wrote:
>> Thanks for your advice. It's indeed more appropriate to use "flush" instead
>> of "cancel" here, I will change it soon.
> I saw your v2. Didn't you forget to change also the function name?
Yes, sorry for losing it.
>
>> I didn't quite get what you mean. Do you mean this patch will cause a change
>> in mechanics, and it is necessary to add an explanation?
>>
>> (After deleting the original cgroup,
>>   Before: the limit of the throttled bios can't be changed and the bios will
>> complete under this limit;
>>   Now: the limit will be canceled and the throttled bios will be flushed
>> immediately.)
> I mean -- can the new mechanics be exploited to bypass throttling by
> sending IO from a process, migrate it between cgroups and rmdir them?
> That should be covered in the commit log.
Yes.
Migrating a process to a new cgroup means we want the next bio will be
throttled by the new limit.
We can flush the throttled bios by deleting the old cgroup, or keep it
to make the previous bios complete slowly under the original limit.


Thanks.

>
> Thanks,
> Michal