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Subject: Re: [PATCH v3 3/3] md: protect md_thread with rcu
To:     Yu Kuai <yukuai1@huaweicloud.com>,
        Logan Gunthorpe <logang@deltatee.com>, song@kernel.org
Cc:     linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
        yi.zhang@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230330202046.795213-1-yukuai1@huaweicloud.com>
 <20230330202046.795213-4-yukuai1@huaweicloud.com>
 <67b0f0fb-e9f3-b716-f22f-0ca091a291b0@deltatee.com>
 <7efda5d2-96bf-05a4-418d-122bfdf2ce04@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <f54452de-c5f2-aeab-1218-c0ed3990a481@huaweicloud.com>
Date:   Fri, 31 Mar 2023 14:36:22 +0800
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Hi,

在 2023/03/31 9:08, Yu Kuai 写道:
> Hi, Logan!
> 
> 在 2023/03/31 3:35, Logan Gunthorpe 写道:
>>
>> A couple points:
>>
>> I don't think we need a double pointer here. rcu_dereference() doesn't
>> actually do anything but annotate the fact that we are accessing a
>> pointer protected by rcu. It does require annotations on that pointer
>> (__rcu) which is checked by sparse (I suspect this patch will produce a
>> lot of sparse errors from kbuild bot).
>>
>> I think all we need is:
>>
>> void md_wakeup_thread(struct md_thread __rcu *rthread)
>> {
>>     struct md_thread *thread;
>>
>>     rcu_read_lock();
>>     thread = rcu_dereference(rthread);
>>     ...
>>     rcu_read_unlock();
>>
>> }
>>
>> The __rcu annotation will have to be added to all the pointers this
>> function is called on as well as to md_register_thread() and
>> md_unregister_thread(). And anything else that uses those pointers.
>> Running sparse on the code and eliminating all new errors for the patch
>> is important.
> 
> Yes, you're right, I'll remove patch 2 and update patch 3. And I'll try
> to run sparse before sending the new version.
> 

By the way, I observed lots of sparse errors and warnings for current
code, will it make sense to fix them?

Thanks,
Kuai