RTC: assure proper memory ordering with respect to RTC_DEV_BUSY flag

We must make sure that the RTC_DEV_BUSY flag has proper lock semantics,
i.e.  that the RTC_DEV_BUSY stores clearing the flag don't get reordered
before the preceeding stores and loads and vice versa.

Spotted by Nick Piggin.

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

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/rtc/rtc-dev.c b/drivers/rtc/rtc-dev.c
index ae1bf177d625..025c60a17a4a 100644
--- a/drivers/rtc/rtc-dev.c
+++ b/drivers/rtc/rtc-dev.c
@@ -26,7 +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;
 
-        if (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
+        if (test_and_set_bit_lock(RTC_DEV_BUSY, &rtc->flags))
                 return -EBUSY;
 
         file->private_data = rtc;
@@ -41,7 +41,7 @@ static int rtc_dev_open(struct inode *inode, struct file *file)
         }
 
         /* something has gone wrong */
-        clear_bit(RTC_DEV_BUSY, &rtc->flags);
+        clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);
         return err;
 }
 
@@ -402,7 +402,7 @@ static int rtc_dev_release(struct inode *inode, struct file *file)
         if (rtc->ops->release)
                 rtc->ops->release(rtc->dev.parent);
 
-        clear_bit(RTC_DEV_BUSY, &rtc->flags);
+        clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);
         return 0;
 }