linux-kernel - Re: [PATCH] hwspinlock: improve locking safety by using raw_spinlock

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Message-ID: <cb11a5b8-8134-4059-b4f8-96aa0e7f7c2f@linux.dev>
Date: Sun, 1 Sep 2024 21:34:37 +0800
From: Wen Yang <wen.yang@...ux.dev>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Dave Young <dyoung@...hat.com>, linux-remoteproc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwspinlock: improve locking safety by using
 raw_spinlock_t



On 2024/8/27 00:37, Bjorn Andersson wrote:
> On Sat, Aug 24, 2024 at 10:38:47PM GMT, Wen Yang wrote:
>> Both __hwspin_trylock and __hwspin_unlock use hwlock->lock, and require
>> running in atomic context, with a special annotation:
>> function will never sleep.
>> However, this requirement is not fulfilled on PREEMPT_RT.
>>
>> To address it, use raw_spinlock_t instead of spin_lock_t.
> 
> I think the "will never sleep" comment expresses that the function can
> be called in atomic or irq context, not necessarily that it must not
> sleep.
> 
> If this is the case, would it be better to fix the comment or the code?
> 

Thank you for your commens.
Let's try updating the following documents:
Documentation/locking/hwspinlock.rst
drivers/hwspinlock/hwspinlock_core.c
include/linux/hwspinlock.h

--
Best wishes,
Wen

> 
>>
>> Signed-off-by: Wen Yang <wen.yang@...ux.dev>
>> Cc: Bjorn Andersson <andersson@...nel.org>
>> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Cc: Dave Young <dyoung@...hat.com>
>> Cc: linux-remoteproc@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>   drivers/hwspinlock/hwspinlock_core.c     | 20 ++++++++++----------
>>   drivers/hwspinlock/hwspinlock_internal.h |  2 +-
>>   2 files changed, 11 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/hwspinlock/hwspinlock_core.c b/drivers/hwspinlock/hwspinlock_core.c
>> index 6505261e6068..76e5a6c645b1 100644
>> --- a/drivers/hwspinlock/hwspinlock_core.c
>> +++ b/drivers/hwspinlock/hwspinlock_core.c
>> @@ -111,17 +111,17 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
>>   	 */
>>   	switch (mode) {
>>   	case HWLOCK_IRQSTATE:
>> -		ret = spin_trylock_irqsave(&hwlock->lock, *flags);
>> +		ret = raw_spin_trylock_irqsave(&hwlock->lock, *flags);
>>   		break;
>>   	case HWLOCK_IRQ:
>> -		ret = spin_trylock_irq(&hwlock->lock);
>> +		ret = raw_spin_trylock_irq(&hwlock->lock);
>>   		break;
>>   	case HWLOCK_RAW:
>>   	case HWLOCK_IN_ATOMIC:
>>   		ret = 1;
>>   		break;
>>   	default:
>> -		ret = spin_trylock(&hwlock->lock);
>> +		ret = raw_spin_trylock(&hwlock->lock);
>>   		break;
>>   	}
>>   
>> @@ -136,17 +136,17 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
>>   	if (!ret) {
>>   		switch (mode) {
>>   		case HWLOCK_IRQSTATE:
>> -			spin_unlock_irqrestore(&hwlock->lock, *flags);
>> +			raw_spin_unlock_irqrestore(&hwlock->lock, *flags);
>>   			break;
>>   		case HWLOCK_IRQ:
>> -			spin_unlock_irq(&hwlock->lock);
>> +			raw_spin_unlock_irq(&hwlock->lock);
>>   			break;
>>   		case HWLOCK_RAW:
>>   		case HWLOCK_IN_ATOMIC:
>>   			/* Nothing to do */
>>   			break;
>>   		default:
>> -			spin_unlock(&hwlock->lock);
>> +			raw_spin_unlock(&hwlock->lock);
>>   			break;
>>   		}
>>   
>> @@ -289,17 +289,17 @@ void __hwspin_unlock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
>>   	/* Undo the spin_trylock{_irq, _irqsave} called while locking */
>>   	switch (mode) {
>>   	case HWLOCK_IRQSTATE:
>> -		spin_unlock_irqrestore(&hwlock->lock, *flags);
>> +		raw_spin_unlock_irqrestore(&hwlock->lock, *flags);
>>   		break;
>>   	case HWLOCK_IRQ:
>> -		spin_unlock_irq(&hwlock->lock);
>> +		raw_spin_unlock_irq(&hwlock->lock);
>>   		break;
>>   	case HWLOCK_RAW:
>>   	case HWLOCK_IN_ATOMIC:
>>   		/* Nothing to do */
>>   		break;
>>   	default:
>> -		spin_unlock(&hwlock->lock);
>> +		raw_spin_unlock(&hwlock->lock);
>>   		break;
>>   	}
>>   }
>> @@ -535,7 +535,7 @@ int hwspin_lock_register(struct hwspinlock_device *bank, struct device *dev,
>>   	for (i = 0; i < num_locks; i++) {
>>   		hwlock = &bank->lock[i];
>>   
>> -		spin_lock_init(&hwlock->lock);
>> +		raw_spin_lock_init(&hwlock->lock);
>>   		hwlock->bank = bank;
>>   
>>   		ret = hwspin_lock_register_single(hwlock, base_id + i);
>> diff --git a/drivers/hwspinlock/hwspinlock_internal.h b/drivers/hwspinlock/hwspinlock_internal.h
>> index f298fc0ee5ad..9fbd66e8a82f 100644
>> --- a/drivers/hwspinlock/hwspinlock_internal.h
>> +++ b/drivers/hwspinlock/hwspinlock_internal.h
>> @@ -42,7 +42,7 @@ struct hwspinlock_ops {
>>    */
>>   struct hwspinlock {
>>   	struct hwspinlock_device *bank;
>> -	spinlock_t lock;
>> +	raw_spinlock_t lock;
>>   	void *priv;
>>   };
>>   
>> -- 
>> 2.25.1
>>