From: Yu Kuai <yukuai1@huaweicloud.com>
To: Tejun Heo <tj@kernel.org>, Yu Kuai <yukuai1@huaweicloud.com>
Cc: hch@infradead.org, josef@toxicpanda.com, axboe@kernel.dk,
cgroups@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
"yukuai (C)" <yukuai3@huawei.com>
Subject: Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg
Date: Thu, 5 Jan 2023 09:14:07 +0800 [thread overview]
Message-ID: <c63ee2ad-23d5-3be0-c731-28494398b391@huaweicloud.com> (raw)
In-Reply-To: <Y7XzUee5Bq+DoIC1@slm.duckdns.org>
Hi,
在 2023/01/05 5:44, Tejun Heo 写道:
> On Tue, Dec 27, 2022 at 08:55:01PM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> iocost requires that child iocg must exit before parent iocg, otherwise
>> kernel might crash in ioc_timer_fn(). However, currently iocg is exited
>> in pd_free_fn(), which can't guarantee such order:
>>
>> 1) remove cgroup can concurrent with deactivate policy;
>> 2) blkg_free() triggered by remove cgroup is asynchronously, remove
>> child cgroup can concurrent with remove parent cgroup;
>>
>> Fix the problem by add refcounting for iocg, and child iocg will grab
>> reference of parent iocg, so that parent iocg will wait for all child
>> iocg to be exited.
>
> Wouldn't it be better to do this refcnting in the blk-cgroup core code
> rather than in blk-iocost?
>
The problem is that I can't find a proper way to fix the competition
that pd_free_fn() can be called from different context:
1) from blkg_free() that is called asynchronously from removing cgroup;
2) from blkcg_deactivate_policy() that is called from removing device;
1) is related to blkg, while 2) is not, hence refcnting from blkg can't
fix the problem. refcnting from blkcg_policy_data should be ok, but I
see that bfq already has the similar refcnting, while other policy
doesn't require such refcnting.
Any suggestions?
Thanks,
Kuai
> Thanks.
>
next prev parent reply other threads:[~2023-01-05 1:15 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-27 12:55 [PATCH v2 0/2] blk-iocost: add refcounting for iocg and ioc Yu Kuai
2022-12-27 12:55 ` [PATCH v2 1/2] blk-iocost: add refcounting for iocg Yu Kuai
2023-01-04 21:44 ` Tejun Heo
2023-01-05 1:14 ` Yu Kuai [this message]
2023-01-05 18:32 ` Tejun Heo
2023-01-06 1:08 ` Yu Kuai
2023-01-06 20:18 ` Tejun Heo
2023-01-09 1:32 ` Yu Kuai
2023-01-09 18:23 ` Tejun Heo
2023-01-10 1:39 ` Yu Kuai
2023-01-10 18:36 ` Tejun Heo
2023-01-11 1:36 ` Yu Kuai
2023-01-11 17:07 ` Tejun Heo
2023-01-12 6:18 ` Yu Kuai
2023-01-13 0:53 ` Tejun Heo
2023-01-13 1:10 ` Yu Kuai
2023-01-13 1:15 ` Tejun Heo
2023-01-13 1:25 ` Yu Kuai
2023-01-13 17:16 ` Tejun Heo
2023-01-16 3:25 ` Yu Kuai
2022-12-27 12:55 ` [PATCH v2 2/2] blk-iocost: add refcounting for ioc Yu Kuai
2023-01-04 21:45 ` Tejun Heo
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