Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 07/10] staging: erofs: separate into init_once / always
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     <devel@driverdev.osuosl.org>, <linux-erofs@lists.ozlabs.org>,
        Chao Yu <yuchao0@huawei.com>,
        LKML <linux-kernel@vger.kernel.org>, <weidu.du@huawei.com>,
        Miao Xie <miaoxie@huawei.com>
References: <20181120143425.43637-1-gaoxiang25@huawei.com>
 <20181120143425.43637-8-gaoxiang25@huawei.com>
 <20181122102339.GG3189@kroah.com>
 <66b90226-5d0e-7344-5220-908aa243b014@huawei.com>
 <20181122110500.GC5287@kroah.com>
From:   Gao Xiang <gaoxiang25@huawei.com>
Message-ID: <ef49bf11-b937-46b4-1b9a-c068182aa7d9@huawei.com>
Date:   Thu, 22 Nov 2018 19:11:08 +0800
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.3.0
MIME-Version: 1.0
In-Reply-To: <20181122110500.GC5287@kroah.com>
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Greg,

On 2018/11/22 19:05, Greg Kroah-Hartman wrote:
> On Thu, Nov 22, 2018 at 06:34:10PM +0800, Gao Xiang wrote:
>> Hi Greg,
>>
>> On 2018/11/22 18:23, Greg Kroah-Hartman wrote:
>>>> +
>>>> +	DBG_BUGON(work->nr_pages);
>>>> +	DBG_BUGON(work->vcnt);
>>> How can these ever be triggered?  I understand the need for debugging
>>> code when you are writing code, but at this point it shouldn't be needed
>>> anymore, right?
>>
>> I need to avoid some fields is not 0 when the new workgroup is created (because
>> work->nr_pages and work->vcnt == 0 usually after the previous workgroup is freed).
>> But that is not obvious, it is promised by the current logic.
> 
> Then delete these lines if they can never happen :)

I don't know how to observe such a race in our beta test and community users.

Because if the kernel is crashed, we could collect the whole kernel dump to observe the memory
and all registers, if we only have some warning, it will be not easy to get the state as early as possible.

Thank,
Gao Xiang

> 
>> In order to not introduce such a issue in the future, or there are some potential
>> race (work->nr_pages and work->vcnt != 0 when the previous workgroup == 0), it need
>> to be noticed to developpers as early as possible.
> 
> Then make it a real call, do not wrap it in odd macros that do not
> really explain why it is "debugging only".  Your code is "real" now,
> make the logic real for all developers and users.
> 
> thanks,
> 
> greg k-h
>