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From: Waiman Long <llong@redhat.com>
To: 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: Sun, 8 Aug 2021 23:01:07 -0400	[thread overview]
Message-ID: <48cddad4-0388-ae8b-f98b-1629b9ae590a@redhat.com> (raw)
In-Reply-To: <20210809021215.19991-1-nixiaoming@huawei.com>

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.
>
> Previously discussed with Peter Zijlstra, see link:
>   https://lore.kernel.org/lkml/20210806082320.GD22037@worktop.programming.kicks-ass.net
>
> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
> ---
>   kernel/locking/semaphore.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
> index 9aa855a96c4a..9ee381e4d2a4 100644
> --- a/kernel/locking/semaphore.c
> +++ b/kernel/locking/semaphore.c
> @@ -54,6 +54,7 @@ void down(struct semaphore *sem)
>   {
>   	unsigned long flags;
>   
> +	might_sleep();
>   	raw_spin_lock_irqsave(&sem->lock, flags);
>   	if (likely(sem->count > 0))
>   		sem->count--;
> @@ -77,6 +78,7 @@ int down_interruptible(struct semaphore *sem)
>   	unsigned long flags;
>   	int result = 0;
>   
> +	might_sleep();
>   	raw_spin_lock_irqsave(&sem->lock, flags);
>   	if (likely(sem->count > 0))
>   		sem->count--;
> @@ -103,6 +105,7 @@ int down_killable(struct semaphore *sem)
>   	unsigned long flags;
>   	int result = 0;
>   
> +	might_sleep();
>   	raw_spin_lock_irqsave(&sem->lock, flags);
>   	if (likely(sem->count > 0))
>   		sem->count--;
> @@ -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.

Cheers,
Longman


  reply	other threads:[~2021-08-09  3:01 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 [this message]
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
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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