locking/arch, s390: 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/150670117817.23930.13068785028558453848.stgit@localhost.localdomainSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/s390/include/asm/rwsem.h

@@ -49,7 +49,7 @@
 /*
  * lock for reading
  */
-static inline void __down_read(struct rw_semaphore *sem)
+static inline int ___down_read(struct rw_semaphore *sem)
 {
 	signed long old, new;
 
@@ -62,10 +62,25 @@ static inline void __down_read(struct rw_semaphore *sem)
 		: "=&d" (old), "=&d" (new), "=Q" (sem->count)
 		: "Q" (sem->count), "i" (RWSEM_ACTIVE_READ_BIAS)
 		: "cc", "memory");
-	if (old < 0)
+	return (old < 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;
+}
+
 /*
  * trylock for reading -- returns 1 if successful, 0 if contention
  */