locking/rwsem, ia64: Provide __down_write_killable()

Introduce ___down_write() for the fast path and reuse it for __down_write()
resp. __down_write_killable() each using the respective generic slow path
(rwsem_down_write_failed() resp. rwsem_down_write_failed_killable()).

Signed-off-by: Michal Hocko <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Chris Zankel <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Max Filippov <[e-mail]>
Cc: Paul E. McKenney <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Signed-off-by: Davidlohr Bueso <[e-mail]>
Cc: Signed-off-by: Jason Low <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Tony Luck <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/ia64/include/asm/rwsem.h

···
 /*
  * lock for writing
  */
-static inline void
-__down_write (struct rw_semaphore *sem)
+static inline long
+___down_write (struct rw_semaphore *sem)
 {
 	long old, new;
 
···
 		new = old + RWSEM_ACTIVE_WRITE_BIAS;
 	} while (cmpxchg_acq(&sem->count, old, new) != old);
 
-	if (old != 0)
+	return old;
+}
+
+static inline void
+__down_write (struct rw_semaphore *sem)
+{
+	if (___down_write(sem))
 		rwsem_down_write_failed(sem);
+}
+
+static inline int
+__down_write_killable (struct rw_semaphore *sem)
+{
+	if (___down_write(sem))
+		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
+			return -EINTR;
+
+	return 0;
 }
 
 /*