[PATCH 1/5][Bionic][SRU Artful] locking/qrwlock: Use 'struct qrwlock' instead of 'struct __qrwlock'

[dann frazier]

From: Will Deacon <will.deacon at arm.com>

BugLink: https://bugs.launchpad.net/bugs/1732238

There's no good reason to keep the internal structure of struct qrwlock
hidden from qrwlock.h, particularly as it's actually needed for unlock
and ends up being abstracted independently behind the __qrwlock_write_byte()
function.

Stop pretending we can hide this stuff, and move the __qrwlock definition
into qrwlock, removing the __qrwlock_write_byte() nastiness and using the
same struct definition everywhere instead.

Signed-off-by: Will Deacon <will.deacon at arm.com>
Acked-by: Peter Zijlstra <peterz at infradead.org>
Cc: Boqun Feng <boqun.feng at gmail.com>
Cc: Jeremy.Linton at arm.com
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Waiman Long <longman at redhat.com>
Cc: linux-arm-kernel at lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
(cherry picked from commit e0d02285f16e8d5810f3d5d5e8a5886ca0015d3b)
Signed-off-by: dann frazier <dann.frazier at canonical.com>
---
 include/asm-generic/qrwlock.h       | 12 +-----------
 include/asm-generic/qrwlock_types.h | 15 +++++++++++++--
 kernel/locking/qrwlock.c            | 26 ++------------------------
 3 files changed, 16 insertions(+), 37 deletions(-)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 7d026bf27713..5a571469f324 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -146,23 +146,13 @@ static inline void queued_read_unlock(struct qrwlock *lock)
 	(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
 }
 
-/**
- * __qrwlock_write_byte - retrieve the write byte address of a queue rwlock
- * @lock : Pointer to queue rwlock structure
- * Return: the write byte address of a queue rwlock
- */
-static inline u8 *__qrwlock_write_byte(struct qrwlock *lock)
-{
-	return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN);
-}
-
 /**
  * queued_write_unlock - release write lock of a queue rwlock
  * @lock : Pointer to queue rwlock structure
  */
 static inline void queued_write_unlock(struct qrwlock *lock)
 {
-	smp_store_release(__qrwlock_write_byte(lock), 0);
+	smp_store_release(&lock->wmode, 0);
 }
 
 /*
diff --git a/include/asm-generic/qrwlock_types.h b/include/asm-generic/qrwlock_types.h
index 0abc6b6062fb..507f2dc51bba 100644
--- a/include/asm-generic/qrwlock_types.h
+++ b/include/asm-generic/qrwlock_types.h
@@ -9,12 +9,23 @@
  */
 
 typedef struct qrwlock {
-	atomic_t		cnts;
+	union {
+		atomic_t cnts;
+		struct {
+#ifdef __LITTLE_ENDIAN
+			u8 wmode;	/* Writer mode   */
+			u8 rcnts[3];	/* Reader counts */
+#else
+			u8 rcnts[3];	/* Reader counts */
+			u8 wmode;	/* Writer mode   */
+#endif
+		};
+	};
 	arch_spinlock_t		wait_lock;
 } arch_rwlock_t;
 
 #define	__ARCH_RW_LOCK_UNLOCKED {		\
-	.cnts = ATOMIC_INIT(0),			\
+	{ .cnts = ATOMIC_INIT(0), },		\
 	.wait_lock = __ARCH_SPIN_LOCK_UNLOCKED,	\
 }
 
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index 2655f26ec882..1af791e37348 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -23,26 +23,6 @@
 #include <linux/spinlock.h>
 #include <asm/qrwlock.h>
 
-/*
- * This internal data structure is used for optimizing access to some of
- * the subfields within the atomic_t cnts.
- */
-struct __qrwlock {
-	union {
-		atomic_t cnts;
-		struct {
-#ifdef __LITTLE_ENDIAN
-			u8 wmode;	/* Writer mode   */
-			u8 rcnts[3];	/* Reader counts */
-#else
-			u8 rcnts[3];	/* Reader counts */
-			u8 wmode;	/* Writer mode   */
-#endif
-		};
-	};
-	arch_spinlock_t	lock;
-};
-
 /**
  * rspin_until_writer_unlock - inc reader count & spin until writer is gone
  * @lock  : Pointer to queue rwlock structure
@@ -125,10 +105,8 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
 	 * or wait for a previous writer to go away.
 	 */
 	for (;;) {
-		struct __qrwlock *l = (struct __qrwlock *)lock;
-
-		if (!READ_ONCE(l->wmode) &&
-		   (cmpxchg_relaxed(&l->wmode, 0, _QW_WAITING) == 0))
+		if (!READ_ONCE(lock->wmode) &&
+		   (cmpxchg_relaxed(&lock->wmode, 0, _QW_WAITING) == 0))
 			break;
 
 		cpu_relax();
-- 
2.15.1