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From: Xiaoming Ni <nixiaoming@huawei.com>
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>
Subject: Re: [PATCH] semaphore: Add might_sleep() to down_*() family
Date: Mon, 9 Aug 2021 22:33:18 +0800	[thread overview]
Message-ID: <2266017d-df76-1208-0e1f-0b066c788f66@huawei.com> (raw)
In-Reply-To: <65fe396a-b10d-2388-8229-05fd43d58927@redhat.com>

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


  reply	other threads:[~2021-08-09 14:36 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09  2:12 Xiaoming Ni
2021-08-09  3:01 ` Waiman Long
2021-08-09  3:51   ` Xiaoming Ni
2021-08-09 12:52     ` Waiman Long
2021-08-09 14:33       ` Xiaoming Ni [this message]
2021-08-13 17:27   ` Thomas Gleixner
2021-08-13 18:47     ` Waiman Long
2021-08-13 14:43 ` Will Deacon
2021-08-23  9:39 ` [tip: locking/core] locking/semaphore: " tip-bot2 for Xiaoming Ni
2021-08-31 11:13 ` [PATCH] semaphore: " Guenter Roeck
2021-08-31 11:39   ` Hanjun Guo
2021-08-31 12:20     ` Thomas Gleixner
2021-08-31 11:40   ` Peter Zijlstra
2021-08-31 12:13   ` Thomas Gleixner
2021-08-31 12:34     ` Will Deacon
2021-08-31 17:42     ` Guenter Roeck
2021-09-01  8:37     ` [tip: smp/urgent] drivers: base: cacheinfo: Get rid of DEFINE_SMP_CALL_CACHE_FUNCTION() tip-bot2 for Thomas Gleixner

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