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Date: Wed, 17 Dec 2014 13:51:50 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Hyogi Gim <hyogi.gim@lge.com>
Cc: a.zummo@towertech.it, rtc-linux@googlegroups.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drivers/rtc/interface.c: check the error after
 __rtc_read_time()
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On Wed, 17 Dec 2014 12:15:24 +0900 Hyogi Gim <hyogi.gim@lge.com> wrote:

> Add the verification code for returned __rtc_read_time() error in
> rtc_update_irq_enable() and rtc_timer_do_work().
> 
> ...
L
> --- a/drivers/rtc/interface.c
> +++ b/drivers/rtc/interface.c
> @@ -489,7 +489,10 @@ int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
>  		struct rtc_time tm;
>  		ktime_t now, onesec;
>  
> -		__rtc_read_time(rtc, &tm);
> +		err = __rtc_read_time(rtc, &tm);
> +		if (err < 0)
> +			goto out;
> +
>  		onesec = ktime_set(1, 0);
>  		now = rtc_tm_to_ktime(tm);
>  		rtc->uie_rtctimer.node.expires = ktime_add(now, onesec);

I'm not sure about this part.  If __rtc_read_time() returns -EINVAL
(due to !rtc->ops->read_time) then rtc_update_irq_enable() will go and
call rtc_dev_update_irq_enable_emul(), inappropriately.

On the other hand, if __rtc_read_time() returns -EINVAL because that's
what rtc->ops->read_time() returned then perhaps
rtc_update_irq_enable() *should* call rtc_dev_update_irq_enable_emul().

Messy.