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Re: [PATCH v3 3/4] genirq: Split irq_set_affinity() so it can be called

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH v3 3/4] genirq: Split irq_set_affinity() so it can be called with lock held
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 25 Mar 2011 23:32:51 +0100 (CET)
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org, linux-kernel@vger.kernel.org
In-reply-to: <1301081931-11240-4-git-send-email-ddaney@caviumnetworks.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1301081931-11240-1-git-send-email-ddaney@caviumnetworks.com> <1301081931-11240-4-git-send-email-ddaney@caviumnetworks.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Alpine 2.00 (LFD 1167 2008-08-23)
On Fri, 25 Mar 2011, David Daney wrote:

> The .irq_cpu_online() and .irq_cpu_offline() functions may need to
> adjust affinity, but they are called with the descriptor lock held.
> Create __irq_set_affinity_locked() which is called with the lock held.
> Make irq_set_affinity() just a wrapper that acquires the lock.
> 
> Signed-off-by: David Daney <ddaney@caviumnetworks.com>
> ---
>  include/linux/interrupt.h |    2 ++
>  kernel/irq/manage.c       |   40 ++++++++++++++++++++++++++--------------
>  2 files changed, 28 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 59b72ca..815f9fb 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -229,6 +229,8 @@ static inline int check_wakeup_irqs(void) { return 0; }
>  extern cpumask_var_t irq_default_affinity;
>  
>  extern int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask);
> +extern int __irq_set_affinity_locked(struct irq_desc *desc,
> +                                  const struct cpumask *cpumask);
>  extern int irq_can_set_affinity(unsigned int irq);
>  extern int irq_select_affinity(unsigned int irq);
>  
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 0a2aa73..3d3bed1 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -139,24 +139,12 @@ static inline void
>  irq_get_pending(struct cpumask *mask, struct irq_desc *desc) { }
>  #endif
>  
> -/**
> - *   irq_set_affinity - Set the irq affinity of a given irq
> - *   @irq:           Interrupt to set affinity
> - *   @cpumask:       cpumask
> - *
> - */
> -int irq_set_affinity(unsigned int irq, const struct cpumask *mask)
> +
> +int __irq_set_affinity_locked(struct irq_desc *desc, const struct cpumask 
> *mask)
>  {
> -     struct irq_desc *desc = irq_to_desc(irq);
>       struct irq_chip *chip = desc->irq_data.chip;
> -     unsigned long flags;
>       int ret = 0;
>  
> -     if (!chip->irq_set_affinity)
> -             return -EINVAL;

We want to keep that check here. No need to crash with a NULL pointer
dereference, when we can deal with it gracefully.

Thanks,

        tglx

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