RTC: convert mutex to bitfield

RTC code is using mutex to assure exclusive access to /dev/rtc.  This is
however wrong usage, as it leaves the mutex locked when returning into
userspace, which is unacceptable.

Convert rtc->char_lock into bit operation.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 10 insertions, 11 deletions

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index de0da545c7a1..a4f56e95cf96 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -293,7 +293,7 @@ int rtc_irq_register(struct rtc_device *rtc, struct rtc_task *task)
                 return -EINVAL;
 
         /* Cannot register while the char dev is in use */
-        if (!(mutex_trylock(&rtc->char_lock)))
+        if (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
                 return -EBUSY;
 
         spin_lock_irq(&rtc->irq_task_lock);
@@ -303,7 +303,7 @@ int rtc_irq_register(struct rtc_device *rtc, struct rtc_task *task)
         }
         spin_unlock_irq(&rtc->irq_task_lock);
 
-        mutex_unlock(&rtc->char_lock);
+        clear_bit(RTC_DEV_BUSY, &rtc->flags);
 
         return retval;
 }
diff --git a/drivers/rtc/rtc-dev.c b/drivers/rtc/rtc-dev.c
index 814583bd2fe7..ae1bf177d625 100644
--- a/drivers/rtc/rtc-dev.c
+++ b/drivers/rtc/rtc-dev.c
@@ -26,10 +26,7 @@ static int rtc_dev_open(struct inode *inode, struct file *file)
                                         struct rtc_device, char_dev);
         const struct rtc_class_ops *ops = rtc->ops;
 
-        /* We keep the lock as long as the device is in use
-         * and return immediately if busy
-         */
-        if (!(mutex_trylock(&rtc->char_lock)))
+        if (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
                 return -EBUSY;
 
         file->private_data = rtc;
@@ -43,8 +40,8 @@ static int rtc_dev_open(struct inode *inode, struct file *file)
                 return 0;
         }
 
-        /* something has gone wrong, release the lock */
-        mutex_unlock(&rtc->char_lock);
+        /* something has gone wrong */
+        clear_bit(RTC_DEV_BUSY, &rtc->flags);
         return err;
 }
 
@@ -405,7 +402,7 @@ static int rtc_dev_release(struct inode *inode, struct file *file)
         if (rtc->ops->release)
                 rtc->ops->release(rtc->dev.parent);
 
-        mutex_unlock(&rtc->char_lock);
+        clear_bit(RTC_DEV_BUSY, &rtc->flags);
         return 0;
 }
 
@@ -440,7 +437,6 @@ void rtc_dev_prepare(struct rtc_device *rtc)
 
         rtc->dev.devt = MKDEV(MAJOR(rtc_devt), rtc->id);
 
-        mutex_init(&rtc->char_lock);
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
         INIT_WORK(&rtc->uie_task, rtc_uie_task);
         setup_timer(&rtc->uie_timer, rtc_uie_timer, (unsigned long)rtc);
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 6d5e4a46781e..f2d0d1527721 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -133,6 +133,9 @@ struct rtc_class_ops {
 #define RTC_DEVICE_NAME_SIZE 20
 struct rtc_task;
 
+/* flags */
+#define RTC_DEV_BUSY 0
+
 struct rtc_device
 {
         struct device dev;
@@ -145,7 +148,7 @@ struct rtc_device
         struct mutex ops_lock;
 
         struct cdev char_dev;
-        struct mutex char_lock;
+        unsigned long flags;
 
         unsigned long irq_data;
         spinlock_t irq_lock;