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, 2 insertions, 2 deletions

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index a4f56e95cf96..f1e00ff54ce8 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 (test_and_set_bit(RTC_DEV_BUSY, &rtc->flags))
+        if (test_and_set_bit_lock(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);
 
-        clear_bit(RTC_DEV_BUSY, &rtc->flags);
+        clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);
 
         return retval;
 }