linux-kernel - Re: [PATCH 4/5] xen: events: dynamically allocate irq info structures

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Date:	Tue, 26 Oct 2010 10:30:27 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, xen-devel@...ts.xensource.com, tglx@...utronix.de
Subject: Re: [PATCH 4/5] xen: events: dynamically allocate irq info
 structures

On Mon, Oct 25, 2010 at 05:23:32PM +0100, Ian Campbell wrote:
> Removes nr_irq sized array allocation at start of day.
> 
> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> ---
>  drivers/xen/events.c |   50 +++++++++++++++++++++++++++++++++++++++++---------
>  1 files changed, 41 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index 94055ea..9b58505 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -56,6 +56,8 @@
>   */
>  static DEFINE_SPINLOCK(irq_mapping_update_lock);
>  
> +static LIST_HEAD(xen_irq_list_head);
> +
>  /* IRQ <-> VIRQ mapping. */
>  static DEFINE_PER_CPU(int [NR_VIRQS], virq_to_irq) = {[0 ... NR_VIRQS-1] = -1};
>  
> @@ -85,6 +87,7 @@ enum xen_irq_type {
>   */
>  struct irq_info
>  {
> +	struct list_head list;
>  	enum xen_irq_type type;	/* type */
>  	unsigned short evtchn;	/* event channel */
>  	unsigned short cpu;	/* cpu bound */
> @@ -103,7 +106,6 @@ struct irq_info
>  #define PIRQ_NEEDS_EOI	(1 << 0)
>  #define PIRQ_SHAREABLE	(1 << 1)
>  
> -static struct irq_info *irq_info;
>  static int *pirq_to_irq;
>  static int nr_pirqs;
>  
> @@ -132,7 +134,7 @@ static struct irq_chip xen_pirq_chip;
>  /* Get info for IRQ */
>  static struct irq_info *info_for_irq(unsigned irq)
>  {
> -	return &irq_info[irq];
> +	return get_irq_data(irq);
>  }
>  
>  /* Constructors for packed IRQ information. */
> @@ -315,7 +317,7 @@ static void bind_evtchn_to_cpu(unsigned int chn, unsigned int cpu)
>  	__clear_bit(chn, cpu_evtchn_mask(cpu_from_irq(irq)));
>  	__set_bit(chn, cpu_evtchn_mask(cpu));
>  
> -	irq_info[irq].cpu = cpu;
> +	info_for_irq(irq)->cpu = cpu;
>  }
>  
>  static void init_evtchn_cpu_bindings(void)
> @@ -428,6 +430,21 @@ static int find_unbound_pirq(void)
>  	return -1;
>  }
>  
> +static void xen_irq_init(unsigned irq)
> +{
> +	struct irq_info *info;
> +
> +	info = kmalloc(sizeof(*info), GFP_KERNEL);
> +	if (info == NULL)
> +		panic("Unable to allocate metadata for IRQ%d\n", irq);

There is a bunch of panic around allocating IRQs. There is one earlier
in xen_irq_alloc too, and I was wondering - would it make sense to
perhaps print an error to both the hypervisor and the kernel and
just return -1 as an IRQ and let the kernel continue with its normal
failure path?

I am thinking just in terms of making the system still be able to
work even if parts of it are busted, instead of just crashing the system.

Not sure which philosophy is domiant in the Linux kernel?

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