locking/arch, ia64: Add __down_read_killable()

Similar to __down_write_killable(), and read killable primitive.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arnd@arndb.de
Cc: avagin@virtuozzo.com
Cc: davem@davemloft.net
Cc: fenghua.yu@intel.com
Cc: gorcunov@virtuozzo.com
Cc: heiko.carstens@de.ibm.com
Cc: hpa@zytor.com
Cc: ink@jurassic.park.msu.ru
Cc: mattst88@gmail.com
Cc: rientjes@google.com
Cc: rth@twiddle.net
Cc: schwidefsky@de.ibm.com
Cc: tony.luck@intel.com
Cc: viro@zeniv.linux.org.uk
Link: http://lkml.kernel.org/r/150670116749.23930.14976888440968191759.stgit@localhost.localdomainSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/ia64/include/asm/rwsem.h

@@ -37,15 +37,31 @@
 /*
  * lock for reading
  */
-static inline void
-__down_read (struct rw_semaphore *sem)
+static inline int
+___down_read (struct rw_semaphore *sem)
 {
 	long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
 
-	if (result < 0)
+	return (result < 0);
+}
+
+static inline void
+__down_read (struct rw_semaphore *sem)
+{
+	if (___down_read(sem))
 		rwsem_down_read_failed(sem);
 }
 
+static inline int
+__down_read_killable (struct rw_semaphore *sem)
+{
+	if (___down_read(sem))
+		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
+			return -EINTR;
+
+	return 0;
+}
+
 /*
  * lock for writing
  */
@@ -72,9 +88,10 @@ __down_write (struct rw_semaphore *sem)
 static inline int
 __down_write_killable (struct rw_semaphore *sem)
 {
-	if (___down_write(sem))
+	if (___down_write(sem)) {
 		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
 			return -EINTR;
+	}
 
 	return 0;
 }