[rtc-linux] [PATCH v2] rtc: armada38x: Fix concurrency access in armada38x_rtc_set_time

[rtc-linux] [PATCH v2] rtc: armada38x: Fix concurrency access in armada38x_rtc_set_time

[Gregory CLEMENT]

While setting the time, the RTC TIME register should not be
accessed. However due to hardware constraints, setting the RTC time
involves sleeping during 100ms. This sleep was done outside the
critical section protected by the spinlock, so it was possible to read
the RTC TIME register and get an incorrect value. This patch
introduces a mutex for protecting the RTC TIME access, unlike the
spinlock it is allowed to sleep in a critical section protected by a
mutex. The RTC STATUS register can still be used from the interrupt
handler but it has no effect on setting the time.

Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: <stable@vger.kernel.org> #v4.0
---
Hi,

The first version of this patch was sent too late to be part of
4.1-rc1. However this fix should be part of 4.1.

Since the first version I added the acked-by from Alexandre and I
rebased the patch onto v4.1-rc1.

Thanks,

Gregory


 drivers/rtc/rtc-armada38x.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/rtc/rtc-armada38x.c b/drivers/rtc/rtc-armada38x.c
index 43e04af39e09..cb70ced7e0db 100644
--- a/drivers/rtc/rtc-armada38x.c
+++ b/drivers/rtc/rtc-armada38x.c
@@ -40,6 +40,13 @@ struct armada38x_rtc {
 	void __iomem	    *regs;
 	void __iomem	    *regs_soc;
 	spinlock_t	    lock;
+	/*
+	 * While setting the time, the RTC TIME register should not be
+	 * accessed. Setting the RTC time involves sleeping during
+	 * 100ms, so a mutex instead of a spinlock is used to protect
+	 * it
+	 */
+	struct mutex	    mutex_time;
 	int		    irq;
 };
 
@@ -59,8 +66,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	struct armada38x_rtc *rtc = dev_get_drvdata(dev);
 	unsigned long time, time_check, flags;
 
-	spin_lock_irqsave(&rtc->lock, flags);
-
+	mutex_lock(&rtc->mutex_time);
 	time = readl(rtc->regs + RTC_TIME);
 	/*
 	 * WA for failing time set attempts. As stated in HW ERRATA if
@@ -71,7 +77,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	if ((time_check - time) > 1)
 		time_check = readl(rtc->regs + RTC_TIME);
 
-	spin_unlock_irqrestore(&rtc->lock, flags);
+	mutex_unlock(&rtc->mutex_time);
 
 	rtc_time_to_tm(time_check, tm);
 
@@ -94,19 +100,12 @@ static int armada38x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	 * then wait for 100ms before writing to the time register to be
 	 * sure that the data will be taken into account.
 	 */
-	spin_lock_irqsave(&rtc->lock, flags);
-
+	mutex_lock(&rtc->mutex_time);
 	rtc_delayed_write(0, rtc, RTC_STATUS);
-
-	spin_unlock_irqrestore(&rtc->lock, flags);
-
 	msleep(100);
-
-	spin_lock_irqsave(&rtc->lock, flags);
-
 	rtc_delayed_write(time, rtc, RTC_TIME);
+	mutex_unlock(&rtc->mutex_time);
 
-	spin_unlock_irqrestore(&rtc->lock, flags);
 out:
 	return ret;
 }
@@ -230,6 +229,7 @@ static __init int armada38x_rtc_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	spin_lock_init(&rtc->lock);
+	mutex_init(&rtc->mutex_time);
 
 	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "rtc");
 	rtc->regs = devm_ioremap_resource(&pdev->dev, res);
-- 
2.1.0

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[rtc-linux] Re: [PATCH v2] rtc: armada38x: Fix concurrency access in armada38x_rtc_set_time

[Andrew Lunn]

On Mon, Apr 27, 2015 at 09:20:15AM +0200, Gregory CLEMENT wrote:
> While setting the time, the RTC TIME register should not be
> accessed. However due to hardware constraints, setting the RTC time
> involves sleeping during 100ms. This sleep was done outside the
> critical section protected by the spinlock, so it was possible to read
> the RTC TIME register and get an incorrect value. This patch
> introduces a mutex for protecting the RTC TIME access, unlike the
> spinlock it is allowed to sleep in a critical section protected by a
> mutex. The RTC STATUS register can still be used from the interrupt
> handler but it has no effect on setting the time.
> 
> Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
> Cc: <stable@vger.kernel.org> #v4.0
> ---
> Hi,
> 
> The first version of this patch was sent too late to be part of
> 4.1-rc1. However this fix should be part of 4.1.
> 
> Since the first version I added the acked-by from Alexandre and I
> rebased the patch onto v4.1-rc1.

Given the extra explanation in the follow up emails, this looks O.K.

Acked-by: Andrew Lunn <andrew@lunn.ch>

	  Andrew

> 
> Thanks,
> 
> Gregory
> 
> 
>  drivers/rtc/rtc-armada38x.c | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-armada38x.c b/drivers/rtc/rtc-armada38x.c
> index 43e04af39e09..cb70ced7e0db 100644
> --- a/drivers/rtc/rtc-armada38x.c
> +++ b/drivers/rtc/rtc-armada38x.c
> @@ -40,6 +40,13 @@ struct armada38x_rtc {
>  	void __iomem	    *regs;
>  	void __iomem	    *regs_soc;
>  	spinlock_t	    lock;
> +	/*
> +	 * While setting the time, the RTC TIME register should not be
> +	 * accessed. Setting the RTC time involves sleeping during
> +	 * 100ms, so a mutex instead of a spinlock is used to protect
> +	 * it
> +	 */
> +	struct mutex	    mutex_time;
>  	int		    irq;
>  };
>  
> @@ -59,8 +66,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
>  	struct armada38x_rtc *rtc = dev_get_drvdata(dev);
>  	unsigned long time, time_check, flags;
>  
> -	spin_lock_irqsave(&rtc->lock, flags);
> -
> +	mutex_lock(&rtc->mutex_time);
>  	time = readl(rtc->regs + RTC_TIME);
>  	/*
>  	 * WA for failing time set attempts. As stated in HW ERRATA if
> @@ -71,7 +77,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
>  	if ((time_check - time) > 1)
>  		time_check = readl(rtc->regs + RTC_TIME);
>  
> -	spin_unlock_irqrestore(&rtc->lock, flags);
> +	mutex_unlock(&rtc->mutex_time);
>  
>  	rtc_time_to_tm(time_check, tm);
>  
> @@ -94,19 +100,12 @@ static int armada38x_rtc_set_time(struct device *dev, struct rtc_time *tm)
>  	 * then wait for 100ms before writing to the time register to be
>  	 * sure that the data will be taken into account.
>  	 */
> -	spin_lock_irqsave(&rtc->lock, flags);
> -
> +	mutex_lock(&rtc->mutex_time);
>  	rtc_delayed_write(0, rtc, RTC_STATUS);
> -
> -	spin_unlock_irqrestore(&rtc->lock, flags);
> -
>  	msleep(100);
> -
> -	spin_lock_irqsave(&rtc->lock, flags);
> -
>  	rtc_delayed_write(time, rtc, RTC_TIME);
> +	mutex_unlock(&rtc->mutex_time);
>  
> -	spin_unlock_irqrestore(&rtc->lock, flags);
>  out:
>  	return ret;
>  }
> @@ -230,6 +229,7 @@ static __init int armada38x_rtc_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  
>  	spin_lock_init(&rtc->lock);
> +	mutex_init(&rtc->mutex_time);
>  
>  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "rtc");
>  	rtc->regs = devm_ioremap_resource(&pdev->dev, res);
> -- 
> 2.1.0
> 

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Re: [rtc-linux] [PATCH v2] rtc: armada38x: Fix concurrency access in armada38x_rtc_set_time

[Alexandre Belloni]

Hi Andrew,

Do you mind sending that one to Linus in the 4.1 cycle?

Thanks!

On 27/04/2015 at 09:20:15 +0200, Gregory CLEMENT wrote :
> While setting the time, the RTC TIME register should not be
> accessed. However due to hardware constraints, setting the RTC time
> involves sleeping during 100ms. This sleep was done outside the
> critical section protected by the spinlock, so it was possible to read
> the RTC TIME register and get an incorrect value. This patch
> introduces a mutex for protecting the RTC TIME access, unlike the
> spinlock it is allowed to sleep in a critical section protected by a
> mutex. The RTC STATUS register can still be used from the interrupt
> handler but it has no effect on setting the time.
> 
> Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
> Cc: <stable@vger.kernel.org> #v4.0
> ---
> Hi,
> 
> The first version of this patch was sent too late to be part of
> 4.1-rc1. However this fix should be part of 4.1.
> 
> Since the first version I added the acked-by from Alexandre and I
> rebased the patch onto v4.1-rc1.
> 
> Thanks,
> 
> Gregory
> 
> 
>  drivers/rtc/rtc-armada38x.c | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-armada38x.c b/drivers/rtc/rtc-armada38x.c
> index 43e04af39e09..cb70ced7e0db 100644
> --- a/drivers/rtc/rtc-armada38x.c
> +++ b/drivers/rtc/rtc-armada38x.c
> @@ -40,6 +40,13 @@ struct armada38x_rtc {
>  	void __iomem	    *regs;
>  	void __iomem	    *regs_soc;
>  	spinlock_t	    lock;
> +	/*
> +	 * While setting the time, the RTC TIME register should not be
> +	 * accessed. Setting the RTC time involves sleeping during
> +	 * 100ms, so a mutex instead of a spinlock is used to protect
> +	 * it
> +	 */
> +	struct mutex	    mutex_time;
>  	int		    irq;
>  };
>  
> @@ -59,8 +66,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
>  	struct armada38x_rtc *rtc = dev_get_drvdata(dev);
>  	unsigned long time, time_check, flags;
>  
> -	spin_lock_irqsave(&rtc->lock, flags);
> -
> +	mutex_lock(&rtc->mutex_time);
>  	time = readl(rtc->regs + RTC_TIME);
>  	/*
>  	 * WA for failing time set attempts. As stated in HW ERRATA if
> @@ -71,7 +77,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
>  	if ((time_check - time) > 1)
>  		time_check = readl(rtc->regs + RTC_TIME);
>  
> -	spin_unlock_irqrestore(&rtc->lock, flags);
> +	mutex_unlock(&rtc->mutex_time);
>  
>  	rtc_time_to_tm(time_check, tm);
>  
> @@ -94,19 +100,12 @@ static int armada38x_rtc_set_time(struct device *dev, struct rtc_time *tm)
>  	 * then wait for 100ms before writing to the time register to be
>  	 * sure that the data will be taken into account.
>  	 */
> -	spin_lock_irqsave(&rtc->lock, flags);
> -
> +	mutex_lock(&rtc->mutex_time);
>  	rtc_delayed_write(0, rtc, RTC_STATUS);
> -
> -	spin_unlock_irqrestore(&rtc->lock, flags);
> -
>  	msleep(100);
> -
> -	spin_lock_irqsave(&rtc->lock, flags);
> -
>  	rtc_delayed_write(time, rtc, RTC_TIME);
> +	mutex_unlock(&rtc->mutex_time);
>  
> -	spin_unlock_irqrestore(&rtc->lock, flags);
>  out:
>  	return ret;
>  }
> @@ -230,6 +229,7 @@ static __init int armada38x_rtc_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  
>  	spin_lock_init(&rtc->lock);
> +	mutex_init(&rtc->mutex_time);
>  
>  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "rtc");
>  	rtc->regs = devm_ioremap_resource(&pdev->dev, res);
> -- 
> 2.1.0
> 
> -- 
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> before submitting a driver.
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-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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