linux-kernel - Re: [PATCH] rtc: Make rtc_update

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Date:	Thu, 9 Apr 2009 15:39:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Atsushi Nemoto <anemo@....ocn.ne.jp>
Cc:	a.zummo@...ertech.it, rtc-linux@...glegroups.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: Make rtc_update_irq callable with irqs enabled

On Tue,  7 Apr 2009 01:50:31 +0900
Atsushi Nemoto <anemo@....ocn.ne.jp> wrote:

> The rtc_update_irq() might be called with irqs enabled, if a interrupt
> handler was registered without IRQF_DISABLED.

Why?  What are the consequences of not merging the patch?  Is it a
bugfix?  If so, what are the user-visible effects of the bug?

See, I need to decide if this patch is needed in 2.6.30 (and earlier),
but the changelog doesn't include enough info to make that decision.

> Use spin_lock_irqsave/spin_unlock_irqrestore instead of
> spin_lock/spin_unlock.
> 
> Signed-off-by: Atsushi Nemoto <anemo@....ocn.ne.jp>
> ---
>  drivers/rtc/interface.c |   10 ++++++----
>  1 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> index 4348c4b..a8641f7 100644
> --- a/drivers/rtc/interface.c
> +++ b/drivers/rtc/interface.c
> @@ -376,14 +376,16 @@ EXPORT_SYMBOL_GPL(rtc_update_irq_enable);
>  void rtc_update_irq(struct rtc_device *rtc,
>  		unsigned long num, unsigned long events)
>  {
> -	spin_lock(&rtc->irq_lock);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&rtc->irq_lock, flags);
>  	rtc->irq_data = (rtc->irq_data + (num << 8)) | events;
> -	spin_unlock(&rtc->irq_lock);
> +	spin_unlock_irqrestore(&rtc->irq_lock, flags);
>  
> -	spin_lock(&rtc->irq_task_lock);
> +	spin_lock_irqsave(&rtc->irq_task_lock, flags);
>  	if (rtc->irq_task)
>  		rtc->irq_task->func(rtc->irq_task->private_data);
> -	spin_unlock(&rtc->irq_task_lock);
> +	spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
>  
>  	wake_up_interruptible(&rtc->irq_queue);
>  	kill_fasync(&rtc->async_queue, SIGIO, POLL_IN);

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