Re: [GIT pull] irq updates for 4.13

[Tony Lindgren <tony@atomide.com>]

* Thomas Gleixner <tglx@linutronix.de> [170711 10:17]:
> On Tue, 11 Jul 2017, Tony Lindgren wrote:
> > * Linus Torvalds <torvalds@linux-foundation.org> [170711 08:40]:
> > > On Tue, Jul 11, 2017 at 7:41 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > > >
> > > > Ah. Now that makes sense.
> > > >
> > > > Unpatched the ordering is:
> > > >
> > > >           chip_bus_lock(desc);
> > > >           irq_request_resources(desc);
> > > 
> > > I *looked* at that ordering and then went "Naah, that makes no sense".
> > > 
> > > But if that's the only issue, how about we just re-order those things
> > > - we still don't need to move the irq_request_resources() into the
> > > spinlock, we just move it to below the chip_bus_lock().
> > > 
> > > IOW, something like the (COMPLETELY UNTEESTED!) attached patch.
> > 
> > Yeah that fixes the issue:
> > 
> > Tested-by: Tony Lindgren <tony@atomide.com>
> > 
> > > This assumes that the chip_bus_lock() thing is still ok for the RT
> > > case, but it looks like it might be: the only other one I looked at
> > > (apart from the gpio-omap one) used a mutex.
> > 
> > Yeah and the ordering below makes more sense to me at least. That is
> > assuming we want to call chip_bus_lock() before we start calling the
> > chip functions :)
> 
> We can do that, just the free path is ugly and does not really work that
> way.

OK

> __free_irq()
> 	....
> 	chip_bus_sync_unlock(desc);
> 	...
> 	synchronize_irq(irq);
> 	...
> 	if (!desc->action) {
> 		irq_release_resources();
> 		irq_remove_timings();
> 	}
> 	mutex_unlock(&desc->request_mutex);
> 
> We can't release request_mutex early otherwise we run into the issue of a
> concurrent request_irq() trying to reuse stuff which we just release, but
> we can't reacquire bus_lock under request_mutex either when we change the
> lock ordering to bus_lock -> desc->request_mutex -> desc->lock.
> 
> We really want to have both the release_resources() and the
> remove_timings() calls outside of the spinlocked region. That's not only a
> RT issue, there have been requests for making the resource call 'sleepable'
> for mainline as well.
> 
> Below is a slightly different fix, which keeps the lock order
> 
>       desc->request_mutex -> bus_lock -> desc->lock
> 
> intact and conditionally reacquired the bus lock for the release call.

Yeah that fixes the issue too:

Tested-by: Tony Lindgren <tony@atomide.com>

Regards,

Tony


> 8<------------------------
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -1036,13 +1036,20 @@ static int irq_request_resources(struct
>  	return c->irq_request_resources ? c->irq_request_resources(d) : 0;
>  }
>  
> -static void irq_release_resources(struct irq_desc *desc)
> +static void irq_release_resources(struct irq_desc *desc, bool buslock)
>  {
>  	struct irq_data *d = &desc->irq_data;
>  	struct irq_chip *c = d->chip;
>  
> -	if (c->irq_release_resources)
> -		c->irq_release_resources(d);
> +	if (!c->irq_release_resources)
> +		return;
> +	if (buslock)
> +		chip_bus_lock(desc);
> +
> +	c->irq_release_resources(d);
> +
> +	if (buslock)
> +		chip_bus_sync_unlock(desc);
>  }
>  
>  static int
> @@ -1168,17 +1175,16 @@ static int
>  		new->flags &= ~IRQF_ONESHOT;
>  
>  	mutex_lock(&desc->request_mutex);
> +	chip_bus_lock(desc);
>  	if (!desc->action) {
>  		ret = irq_request_resources(desc);
>  		if (ret) {
>  			pr_err("Failed to request resources for %s (irq %d) on irqchip %s\n",
>  			       new->name, irq, desc->irq_data.chip->name);
> -			goto out_mutex;
> +			goto out_bus;
>  		}
>  	}
>  
> -	chip_bus_lock(desc);
> -
>  	/*
>  	 * The following block of code has to be executed atomically
>  	 */
> @@ -1286,10 +1292,8 @@ static int
>  			ret = __irq_set_trigger(desc,
>  						new->flags & IRQF_TRIGGER_MASK);
>  
> -			if (ret) {
> -				irq_release_resources(desc);
> +			if (ret)
>  				goto out_unlock;
> -			}
>  		}
>  
>  		desc->istate &= ~(IRQS_AUTODETECT | IRQS_SPURIOUS_DISABLED | \
> @@ -1385,12 +1389,10 @@ static int
>  out_unlock:
>  	raw_spin_unlock_irqrestore(&desc->lock, flags);
>  
> -	chip_bus_sync_unlock(desc);
> -
>  	if (!desc->action)
> -		irq_release_resources(desc);
> -
> -out_mutex:
> +		irq_release_resources(desc, false);
> +out_bus:
> +	chip_bus_sync_unlock(desc);
>  	mutex_unlock(&desc->request_mutex);
>  
>  out_thread:
> @@ -1472,6 +1474,7 @@ static struct irqaction *__free_irq(unsi
>  			WARN(1, "Trying to free already-free IRQ %d\n", irq);
>  			raw_spin_unlock_irqrestore(&desc->lock, flags);
>  			chip_bus_sync_unlock(desc);
> +			mutex_unlock(&desc->request_mutex);
>  			return NULL;
>  		}
>  
> @@ -1531,7 +1534,7 @@ static struct irqaction *__free_irq(unsi
>  	}
>  
>  	if (!desc->action) {
> -		irq_release_resources(desc);
> +		irq_release_resources(desc, true);
>  		irq_remove_timings(desc);
>  	}
>  
> 
> 
> 
> 
> 
>