netdev - Re: e1000_netpoll(): disable_irq() triggers might

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Message-ID: <alpine.DEB.2.11.1410292046270.5308@nanos>
Date:	Wed, 29 Oct 2014 20:49:03 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jeffrey.t.kirsher@...el.com
Subject: Re: e1000_netpoll(): disable_irq() triggers might_sleep() on
 linux-next

On Wed, 29 Oct 2014, Peter Zijlstra wrote:

> On Wed, Oct 29, 2014 at 07:33:00PM +0100, Thomas Gleixner wrote:
> > Yuck. No. You are just papering over the problem.
> > 
> > What happens if you add 'threadirqs' to the kernel command line? Or if
> > the interrupt line is shared with a real threaded interrupt user?
> > 
> > The proper solution is to have a poll_lock for e1000 which serializes
> > the hardware interrupt against netpoll instead of using
> > disable/enable_irq().
> > 
> > In fact that's less expensive than the disable/enable_irq() dance and
> > the chance of contention is pretty low. If done right it will be a
> > NOOP for the CONFIG_NET_POLL_CONTROLLER=n case.
> > 
> 
> OK a little something like so then I suppose.. But I suspect most all
> the network drivers will need this and maybe more, disable_irq() is a
> popular little thing and we 'just' changed semantics on them.

We changed that almost 4 years ago :) What we 'just' did was to add a
prominent warning into the code.
 
> ---
>  drivers/net/ethernet/intel/e1000/e1000.h      |  2 ++
>  drivers/net/ethernet/intel/e1000/e1000_main.c | 22 +++++++++++++++++-----
>  kernel/irq/manage.c                           |  2 +-
>  3 files changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/e1000/e1000.h b/drivers/net/ethernet/intel/e1000/e1000.h
> index 69707108d23c..3f48609f2318 100644
> --- a/drivers/net/ethernet/intel/e1000/e1000.h
> +++ b/drivers/net/ethernet/intel/e1000/e1000.h
> @@ -323,6 +323,8 @@ struct e1000_adapter {
>  	struct delayed_work watchdog_task;
>  	struct delayed_work fifo_stall_task;
>  	struct delayed_work phy_info_task;
> +
> +	spinlock_t irq_lock;
>  };
>  
>  enum e1000_state_t {
> diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
> index 5f6aded512f5..d12cbffe2149 100644
> --- a/drivers/net/ethernet/intel/e1000/e1000_main.c
> +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
> @@ -1310,6 +1310,7 @@ static int e1000_sw_init(struct e1000_adapter *adapter)
>  	e1000_irq_disable(adapter);
>  
>  	spin_lock_init(&adapter->stats_lock);
> +	spin_lock_init(&adapter->irq_lock);
>  
>  	set_bit(__E1000_DOWN, &adapter->flags);
>  
> @@ -3748,10 +3749,8 @@ void e1000_update_stats(struct e1000_adapter *adapter)
>   * @irq: interrupt number
>   * @data: pointer to a network interface device structure
>   **/
> -static irqreturn_t e1000_intr(int irq, void *data)
> +static irqreturn_t __e1000_intr(int irq, struct e1000_adapter *adapter)
>  {
> -	struct net_device *netdev = data;
> -	struct e1000_adapter *adapter = netdev_priv(netdev);
>  	struct e1000_hw *hw = &adapter->hw;
>  	u32 icr = er32(ICR);
>  
> @@ -3793,6 +3792,19 @@ static irqreturn_t e1000_intr(int irq, void *data)
>  	return IRQ_HANDLED;
>  }
>  
> +static irqreturn_t e1000_intr(int irq, void *data)
> +{
> +	struct net_device *netdev = data;
> +	struct e1000_adapter *adapter = netdev_priv(netdev);
> +	irqreturn_t ret;
> +
> +	spin_lock(&adapter->irq_lock);
> +	ret = __e1000_intr(irq, adapter);
> +	spin_unlock(&adapter->irq_lock);
> +
> +	return ret;
> +}
> +
>  /**
>   * e1000_clean - NAPI Rx polling callback
>   * @adapter: board private structure
> @@ -5217,9 +5229,9 @@ static void e1000_netpoll(struct net_device *netdev)
>  {
>  	struct e1000_adapter *adapter = netdev_priv(netdev);
>  
> -	disable_irq(adapter->pdev->irq);
> +	spin_lock(&adapter->irq_lock)
>  	e1000_intr(adapter->pdev->irq, netdev);
> -	enable_irq(adapter->pdev->irq);
> +	spin_unlock(&adapter->irq_lock)
>  }
>  #endif
>  
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 0a9104b4608b..b5a4a06bf2fd 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -427,7 +427,7 @@ EXPORT_SYMBOL(disable_irq_nosync);
>   *	to complete before returning. If you use this function while
>   *	holding a resource the IRQ handler may need you will deadlock.
>   *
> - *	This function may be called - with care - from IRQ context.
> + *	This function may _NOT_ be called from IRQ context.

It can only be called from preemptible thread context.

Thanks,

	tglx
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