Re: xen: IPI interrupts not resumed early enough on suspend/resume

[Ian Campbell <Ian.Campbell@citrix.com>]

Ping? The original issue has made it into longterm-2.6.32.y and then
onto Debian (bug #644604) so people keep asking me about it...

Ian.

On Mon, 2011-10-10 at 14:06 +0100, Ian Campbell wrote:
> From dc8a8329f3e97f30e1290c898c816250aa7e8957 Mon Sep 17 00:00:00 2001
> From: Ian Campbell <ian.campbell@citrix.com>
> Date: Mon, 3 Oct 2011 15:37:00 +0100
> Subject: [PATCH] irq: add IRQF_RESUME_EARLY and resume such IRQs earlier in the process
> 
> This adds a mechanism to resume selected IRQs during syscore_resume instead of
> dpm_resume_noirq.
> 
> Under Xen we need to resume IRQs associated with IPIs early enough that the
> resched IPI is unmasked and we can therefore schedule ourselves out of the
> stop_machine where the suspend/resume takes place.
> 
> This issue was introduced by 676dc3cf5bc3 "xen: Use IRQF_FORCE_RESUME".
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Rafael J. Wysocki <rjw@sisk.pl>
> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: xen-devel <xen-devel@lists.xensource.com>
> Cc: stable@kernel.org (at least to 2.6.32.y)
> ---
>  drivers/xen/events.c      |    2 +-
>  include/linux/interrupt.h |    3 ++
>  kernel/irq/pm.c           |   48 ++++++++++++++++++++++++++++++++++++++------
>  3 files changed, 45 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index 7523719..44490de 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -1021,7 +1021,7 @@ int bind_ipi_to_irqhandler(enum ipi_vector ipi,
>  	if (irq < 0)
>  		return irq;
>  
> -	irqflags |= IRQF_NO_SUSPEND | IRQF_FORCE_RESUME;
> +	irqflags |= IRQF_NO_SUSPEND | IRQF_FORCE_RESUME | IRQF_EARLY_RESUME;
>  	retval = request_irq(irq, handler, irqflags, devname, dev_id);
>  	if (retval != 0) {
>  		unbind_from_irq(irq);
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index a103732..f51a81b 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -59,6 +59,8 @@
>   * IRQF_NO_SUSPEND - Do not disable this IRQ during suspend
>   * IRQF_FORCE_RESUME - Force enable it on resume even if IRQF_NO_SUSPEND is set
>   * IRQF_NO_THREAD - Interrupt cannot be threaded
> + * IRQF_EARLY_RESUME - Resume IRQ early during syscore instead of at device
> + *                resume time.
>   */
>  #define IRQF_DISABLED		0x00000020
>  #define IRQF_SAMPLE_RANDOM	0x00000040
> @@ -72,6 +74,7 @@
>  #define IRQF_NO_SUSPEND		0x00004000
>  #define IRQF_FORCE_RESUME	0x00008000
>  #define IRQF_NO_THREAD		0x00010000
> +#define IRQF_EARLY_RESUME	0x00020000
>  
>  #define IRQF_TIMER		(__IRQF_TIMER | IRQF_NO_SUSPEND | IRQF_NO_THREAD)
>  
> diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
> index f76fc00..86bcd79 100644
> --- a/kernel/irq/pm.c
> +++ b/kernel/irq/pm.c
> @@ -9,6 +9,7 @@
>  #include <linux/irq.h>
>  #include <linux/module.h>
>  #include <linux/interrupt.h>
> +#include <linux/syscore_ops.h>
>  
>  #include "internals.h"
>  
> @@ -39,25 +40,58 @@ void suspend_device_irqs(void)
>  }
>  EXPORT_SYMBOL_GPL(suspend_device_irqs);
>  
> -/**
> - * resume_device_irqs - enable interrupt lines disabled by suspend_device_irqs()
> - *
> - * Enable all interrupt lines previously disabled by suspend_device_irqs() that
> - * have the IRQS_SUSPENDED flag set.
> - */
> -void resume_device_irqs(void)
> +static resume_irqs(bool want_early)
>  {
>  	struct irq_desc *desc;
>  	int irq;
>  
>  	for_each_irq_desc(irq, desc) {
>  		unsigned long flags;
> +		bool is_early = desc->action &&
> +			desc->action->flags & IRQF_EARLY_RESUME;
> +
> +		if (is_early != want_early)
> +			continue;
>  
>  		raw_spin_lock_irqsave(&desc->lock, flags);
>  		__enable_irq(desc, irq, true);
>  		raw_spin_unlock_irqrestore(&desc->lock, flags);
>  	}
>  }
> +
> +/**
> + * irq_pm_syscore_ops - enable interrupt lines early
> + *
> + * Enable all interrupt lines with %IRQF_EARLY_RESUME set.
> + */
> +static void irq_pm_syscore_resume(void)
> +{
> +	resume_irqs(true);
> +}
> +
> +static struct syscore_ops irq_pm_syscore_ops = {
> +	.resume		= irq_pm_syscore_resume,
> +};
> +
> +static int __init irq_pm_init_ops(void)
> +{
> +	register_syscore_ops(&irq_pm_syscore_ops);
> +	return 0;
> +}
> +
> +device_initcall(irq_pm_init_ops);
> +
> +/**
> + * resume_device_irqs - enable interrupt lines disabled by suspend_device_irqs()
> + *
> + * Enable all non-%IRQF_EARLY_RESUME interrupt lines previously
> + * disabled by suspend_device_irqs() that have the IRQS_SUSPENDED flag
> + * set as well as those with %IRQF_FORCE_RESUME.
> + */
> +void resume_device_irqs(void)
> +{
> +	resume_irqs(false);
> +}
>  EXPORT_SYMBOL_GPL(resume_device_irqs);
>  
>  /**