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Subject: Re: [PATCH] semaphore: Add might_sleep() to down_*() family
To:     Waiman Long <llong@redhat.com>, <linux-kernel@vger.kernel.org>,
        <peterz@infradead.org>, <mingo@redhat.com>, <will@kernel.org>,
        <boqun.feng@gmail.com>
CC:     <wangle6@huawei.com>, <xiaoqian9@huawei.com>, <shaolexi@huawei.com>
References: <20210809021215.19991-1-nixiaoming@huawei.com>
 <48cddad4-0388-ae8b-f98b-1629b9ae590a@redhat.com>
 <1a5b0f50-b071-2d1c-5277-b6d7f652c257@huawei.com>
 <65fe396a-b10d-2388-8229-05fd43d58927@redhat.com>
From:   Xiaoming Ni <nixiaoming@huawei.com>
Message-ID: <2266017d-df76-1208-0e1f-0b066c788f66@huawei.com>
Date:   Mon, 9 Aug 2021 22:33:18 +0800
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On 2021/8/9 20:52, Waiman Long wrote:
> On 8/8/21 11:51 PM, Xiaoming Ni wrote:
>> On 2021/8/9 11:01, Waiman Long wrote:
>>>
>>> I think it is simpler to just put a "might_sleep()" in 
>>> __down_common() which is the function where sleep can actually happen.
>>>
>>
>> If the actual atomic context hibernation occurs, the corresponding 
>> alarm log is generated in __schedule_bug().
>>     __schedule()
>>         --> schedule_debug()
>>             --> __schedule_bug()
>>
>> However, "might_sleep()" indicates the possibility of sleep, so that 
>> code writers can identify and fix the problem as soon as possible, but 
>> does not trigger atomic context sleep.
>>
>> Is it better to put "might_sleep()" in each down API entry than 
>> __down_common() to help identify potential code problems? 
> 
> Putting "might_sleep()" in each down_*() functions mean that whenever we 
> add a new API function, we have to remember to add "might_sleep()". If
> we put it in down_common(), it will work for any newly added API 
> function in the future even though I doubt we will add any.
> 
If the code enters down_common(), it is not "might" sleep but "will" 
sleep, and an alarm is printed in __schedule_bug() later.

"might_sleep()" is used to check potential problems, and 
"_schedule_bug()" is used to check actual faults.

So, I still think we should add "might_sleep()" to each down_*() 
function to alert code owner to potential problems early.

Thanks
Xiaoming Ni