linux-kernel - [PATCH 4.0 06/60] rtc: armada38x: fix concurrency access in armada38x_rtc_set

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Date:	Fri, 15 May 2015 16:14:07 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.0 06/60] rtc: armada38x: fix concurrency access in armada38x_rtc_set_time

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gregory CLEMENT <gregory.clement@...e-electrons.com>

commit 489405fe5ed38e65f6f82f131a39c67f3bae6045 upstream.

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.

Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Acked-by: Andrew Lunn <andrew@...n.ch>
Cc: Alessandro Zummo <a.zummo@...ertech.it>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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);


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