Subject: Re: [RFC PATCH net-next 00/11] net: remove disable_irq() from ->ndo_poll_controller

From: Sabrina Dubroca <[email-masked]>
Date: Thu, 5 Feb 2015 16:33:00 +0100

2015-02-05, 14:06:23 +0100, Peter Zijlstra wrote:
> On Thu, Feb 05, 2015 at 01:20:59AM +0100, Sabrina Dubroca wrote:
> > Thomas, ping?
> > 
> > thread is over there if you need it:
> > https://marc.info/?l=linux-netdev&m=141833435000554&w=2
> 
> It appears to me you have addressed most his issues and since it appears
> to me the existing synchronze_hardirq() seems to be mostly what we need
> I'll propose (and merge) the below and will take flames from tglx when
> he returns :-)

Great, thanks a lot Peter!

I will prepare the drivers patches based on this.

David, do you want one patch for each driver, or do you want me to group the changes?
There are 60+ drivers to patch, and almost all the patches are just:

-	disable_irq(irq);
-	handler(a, b);
+	if (disable_hardirq(irq))
+		handler(a,b);

> ---
> Subject: genirq: Provide disable_hardirq()
> 
> For things like netpoll there is a need to disable an interrupt from
> atomic context. Currently netpoll uses disable_irq() which will
> sleep-wait on threaded handlers and thus forced_irqthreads breaks
> things.
> 
> Provide disable_hardirq(), which uses synchronize_hardirq() to only wait
> for active hardirq handlers; also change synchronize_hardirq() to
> return the status of threaded handlers.
> 
> This will allow one to try-disable an interrupt from atomic context, or
> in case of request_threaded_irq() to only wait for the hardirq part.
> 
> Suggested-by: Sabrina Dubroca <[email-masked]>
> Signed-off-by: Peter Zijlstra (Intel) <[email-masked]>
> ---
>  include/linux/hardirq.h   |  2 +-
>  include/linux/interrupt.h |  1 +
>  kernel/irq/manage.c       | 36 ++++++++++++++++++++++++++++++++++--
>  3 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index cba442ec3c66..f4af03404b97 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -9,7 +9,7 @@
>  
>  
>  extern void synchronize_irq(unsigned int irq);
> -extern void synchronize_hardirq(unsigned int irq);
> +extern bool synchronize_hardirq(unsigned int irq);
>  
>  #if defined(CONFIG_TINY_RCU)
>  
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index d9b05b5bf8c7..3bb01b9a379c 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -184,6 +184,7 @@ extern void devm_free_irq(struct device *dev, unsigned int irq, void *dev_id);
>  #endif
>  
>  extern void disable_irq_nosync(unsigned int irq);
> +extern bool disable_hardirq(unsigned int irq);
>  extern void disable_irq(unsigned int irq);
>  extern void disable_percpu_irq(unsigned int irq);
>  extern void enable_irq(unsigned int irq);
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index f038e586a4b9..1309cccd714f 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -68,14 +68,20 @@ static void __synchronize_hardirq(struct irq_desc *desc)
>   *	Do not use this for shutdown scenarios where you must be sure
>   *	that all parts (hardirq and threaded handler) have completed.
>   *
> + *	Returns: false if a theaded handler is active.
> + *
>   *	This function may be called - with care - from IRQ context.
>   */
> -void synchronize_hardirq(unsigned int irq)
> +bool synchronize_hardirq(unsigned int irq)
>  {
>  	struct irq_desc *desc = irq_to_desc(irq);
>  
> -	if (desc)
> +	if (desc) {
>  		__synchronize_hardirq(desc);
> +		return !atomic_read(&desc->threads_active);
> +	}
> +
> +	return true;
>  }
>  EXPORT_SYMBOL(synchronize_hardirq);
>  
> @@ -439,6 +445,32 @@ void disable_irq(unsigned int irq)
>  }
>  EXPORT_SYMBOL(disable_irq);
>  
> +/**
> + *	disable_hardirq - disables an irq and waits for hardirq completion
> + *	@irq: Interrupt to disable
> + *
> + *	Disable the selected interrupt line.  Enables and Disables are
> + *	nested.
> + *	This function waits for any pending hard IRQ handlers for this
> + *	interrupt to complete before returning. If you use this function while
> + *	holding a resource the hard IRQ handler may need you will deadlock.
> + *
> + *	When used to optimistically disable an interrupt from atomic context
> + *	the return value must be checked.
> + *
> + *	Returns: false if a theaded handler is active.
> + *
> + *	This function may be called - with care - from IRQ context.
> + */
> +bool disable_hardirq(unsigned int irq)
> +{
> +	if (!__disable_irq_nosync(irq))
> +		return synchronize_hardirq(irq);
> +
> +	return false;
> +}
> +EXPORT_SYMBOL(disable_hardirq);
> +
>  void __enable_irq(struct irq_desc *desc, unsigned int irq)
>  {
>  	switch (desc->depth) {
> --
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-- 
Sabrina