Re: [PATCH] hwspinlock: improve locking safety by using raw_spinlock_t

[Wen Yang]

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@xxxxxxxxx>
> > Cc: Bjorn Andersson <andersson@xxxxxxxxxx>
> > Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > Cc: Dave Young <dyoung@xxxxxxxxxx>
> > Cc: linux-remoteproc@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >   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