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Date:   Fri, 23 Dec 2016 19:34:38 -0600
From:   Suman Anna <s-anna@...com>
To:     Grygorii Strashko <grygorii.strashko@...com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Jason Cooper <jason@...edaemon.net>
CC:     <linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Sam Nelson <sam.nelson@...com>, <bigeasy@...utronix.de>
Subject: Re: [PATCH] irqchip: keystone: Fix "scheduling while atomic" on rt

Hi Grygorii,

On 12/08/2016 05:33 PM, Grygorii Strashko wrote:
> From: "Strashko, Grygorii" <grygorii.strashko@...com>
> 
> The below call chain generates "scheduling while atomic" backtrace and
> causes system crash when Keystone 2 IRQ chip driver is used with RT-kernel:
> 
> gic_handle_irq()
>  |-__handle_domain_irq()
>   |-generic_handle_irq()
>    |-keystone_irq_handler()
>     |-regmap_read()
>      |-regmap_lock_spinlock()
>       |-rt_spin_lock()
> 
> The reason is that Keystone driver dispatches IRQ using chained IRQ handler
> and accesses I/O memory through syscon->regmap(mmio) which is implemented
> as fast_io regmap and uses regular spinlocks for synchronization, but
> spinlocks transformed to rt_mutexes on RT.
> 
> Hence, convert Keystone 2 IRQ driver to use generic irq handler instead of
> chained IRQ handler. This way it will be compatible with RT kernel where it
> will be forced thread IRQ handler while in non-RT kernel it still will be
> executed in HW IRQ context.
> 
> Cc: Suman Anna <s-anna@...com>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> ---
> Hi,
> 
> In general, there is an option to convert this driver to use nested threaded
> irq handlers (this should not affect our current user of these irqs from
> performance point of view), but that will affect on our current remoteproc and
> UIO based drivers (including uio core) which do not expect to use threaded
> irq and use request_irq(). These drivers and UIO core might require to be
> updated to use threaded irqs and (or) request_any_context_irq().
> 
> Suman, what do you think?

I like the current patch as is as we do not want the downstream
subsystems/interrupt users of this driver to change their design
semantics to have to use threaded irqs, and cause a cascading effect.

Tested-by: Suman Anna <s-anna@...com>

regards
Suman



> 
>  drivers/irqchip/irq-keystone.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-keystone.c b/drivers/irqchip/irq-keystone.c
> index 54a5e87..efbcf84 100644
> --- a/drivers/irqchip/irq-keystone.c
> +++ b/drivers/irqchip/irq-keystone.c
> @@ -19,9 +19,9 @@
>  #include <linux/bitops.h>
>  #include <linux/module.h>
>  #include <linux/moduleparam.h>
> +#include <linux/interrupt.h>
>  #include <linux/irqdomain.h>
>  #include <linux/irqchip.h>
> -#include <linux/irqchip/chained_irq.h>
>  #include <linux/of.h>
>  #include <linux/of_platform.h>
>  #include <linux/mfd/syscon.h>
> @@ -39,6 +39,7 @@ struct keystone_irq_device {
>  	struct irq_domain	*irqd;
>  	struct regmap		*devctrl_regs;
>  	u32			devctrl_offset;
> +	raw_spinlock_t		wa_lock;
>  };
>  
>  static inline u32 keystone_irq_readl(struct keystone_irq_device *kirq)
> @@ -83,17 +84,15 @@ static void keystone_irq_ack(struct irq_data *d)
>  	/* nothing to do here */
>  }
>  
> -static void keystone_irq_handler(struct irq_desc *desc)
> +static irqreturn_t keystone_irq_handler(int irq, void *keystone_irq)
>  {
> -	unsigned int irq = irq_desc_get_irq(desc);
> -	struct keystone_irq_device *kirq = irq_desc_get_handler_data(desc);
> +	struct keystone_irq_device *kirq = keystone_irq;
> +	unsigned long wa_lock_flags;
>  	unsigned long pending;
>  	int src, virq;
>  
>  	dev_dbg(kirq->dev, "start irq %d\n", irq);
>  
> -	chained_irq_enter(irq_desc_get_chip(desc), desc);
> -
>  	pending = keystone_irq_readl(kirq);
>  	keystone_irq_writel(kirq, pending);
>  
> @@ -111,13 +110,15 @@ static void keystone_irq_handler(struct irq_desc *desc)
>  			if (!virq)
>  				dev_warn(kirq->dev, "spurious irq detected hwirq %d, virq %d\n",
>  					 src, virq);
> +			raw_spin_lock_irqsave(&kirq->wa_lock, wa_lock_flags);
>  			generic_handle_irq(virq);
> +			raw_spin_unlock_irqrestore(&kirq->wa_lock,
> +						   wa_lock_flags);
>  		}
>  	}
>  
> -	chained_irq_exit(irq_desc_get_chip(desc), desc);
> -
>  	dev_dbg(kirq->dev, "end irq %d\n", irq);
> +	return IRQ_HANDLED;
>  }
>  
>  static int keystone_irq_map(struct irq_domain *h, unsigned int virq,
> @@ -182,9 +183,16 @@ static int keystone_irq_probe(struct platform_device *pdev)
>  		return -ENODEV;
>  	}
>  
> +	raw_spin_lock_init(&kirq->wa_lock);
> +
>  	platform_set_drvdata(pdev, kirq);
>  
> -	irq_set_chained_handler_and_data(kirq->irq, keystone_irq_handler, kirq);
> +	ret = request_irq(kirq->irq, keystone_irq_handler,
> +			  0, dev_name(dev), kirq);
> +	if (ret) {
> +		irq_domain_remove(kirq->irqd);
> +		return ret;
> +	}
>  
>  	/* clear all source bits */
>  	keystone_irq_writel(kirq, ~0x0);
> @@ -199,6 +207,8 @@ static int keystone_irq_remove(struct platform_device *pdev)
>  	struct keystone_irq_device *kirq = platform_get_drvdata(pdev);
>  	int hwirq;
>  
> +	free_irq(kirq->irq, kirq);
> +
>  	for (hwirq = 0; hwirq < KEYSTONE_N_IRQ; hwirq++)
>  		irq_dispose_mapping(irq_find_mapping(kirq->irqd, hwirq));
>  
> 

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