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From: Waiman Long <llong@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <llong@redhat.com>,
	Xiaoming Ni <nixiaoming@huawei.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: Fri, 13 Aug 2021 14:47:35 -0400	[thread overview]
Message-ID: <41bddbee-948a-987c-eb72-108a465a7082@redhat.com> (raw)
In-Reply-To: <877dgpp852.ffs@tglx>

On 8/13/21 1:27 PM, Thomas Gleixner wrote:
> On Sun, Aug 08 2021 at 23:01, Waiman Long wrote:
>> On 8/8/21 10:12 PM, Xiaoming Ni wrote:
>>> Semaphore is sleeping lock. Add might_sleep() to down*() family
>>> (with exception of down_trylock()) to detect atomic context sleep.
>>> @@ -157,6 +160,7 @@ int down_timeout(struct semaphore *sem, long timeout)
>>>    	unsigned long flags;
>>>    	int result = 0;
>>>    
>>> +	might_sleep();
>>>    	raw_spin_lock_irqsave(&sem->lock, flags);
>>>    	if (likely(sem->count > 0))
>>>    		sem->count--;
>> I think it is simpler to just put a "might_sleep()" in __down_common()
>> which is the function where sleep can actually happen.
> No. Putting it in __down_common() is wrong, because that covers only the
> contended case.
>
> But we want to cover the potential sleep, i.e. checking even in the
> non-contended case, which is what might_sleep() is about.

You are right. Thanks for the correction.

Cheers,
Longman


  reply	other threads:[~2021-08-13 18:47 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
2021-08-13 17:27   ` Thomas Gleixner
2021-08-13 18:47     ` Waiman Long [this message]
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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