[PATCH] locking/qrwlock: Let qrwlock has same layout regardless of the endian

[Pan Xinhui]

This patch aims to get rid of endianness in queued_write_unlock(). We
want to set  __qrwlock->wmode to NULL, however the address is not
&lock->cnts in big endian machine. That causes queued_write_unlock()
write NULL to the wrong field of __qrwlock.

Actually qrwlock can have same layout, IOW we can remove the #if
__little_endian in struct __qrwlock. With such modification, we only
need define some _QW* and _QR* with corresponding values in different
endian systems.

Suggested-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Pan Xinhui <xinhui....@linux.vnet.ibm.com>
---
 include/asm-generic/qrwlock.h | 15 +++++++++++----
 kernel/locking/qrwlock.c      | 10 ++++------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 54a8e65..b135c11 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -27,11 +27,18 @@
 /*
  * Writer states & reader shift and bias
  */
-#define        _QW_WAITING     1               /* A writer is waiting     */
-#define        _QW_LOCKED      0xff            /* A writer holds the lock */
-#define        _QW_WMASK       0xff            /* Writer mask             */
+#ifdef __LITTLE_ENDIAN
 #define        _QR_SHIFT       8               /* Reader count shift      */
-#define _QR_BIAS       (1U << _QR_SHIFT)
+#define        _QW_SHIFF       0               /* Writer mode shift    */
+#else
+#define        _QR_SHIFT       0               /* Reader count shift      */
+#define        _QW_SHIFT       24              /* Writer mode shift    */
+#endif
+
+#define        _QW_WAITING     (1U << _QW_SHIFT)       /* A writer is waiting  
   */
+#define        _QW_LOCKED      (0xffU << _QW_SHIFT)    /* A writer holds the 
lock */
+#define        _QW_WMASK       (0xffU << _QW_SHIFT)    /* Writer mask          
   */
+#define        _QR_BIAS        (1U << _QR_SHIFT)
 
 /*
  * External function declarations
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index fec0823..57d66cf 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -30,18 +30,15 @@ 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;
 };
 
+#define        _QW_MODEVAL(v)  ((v) >> _QW_SHIFT)
+
 /**
  * rspin_until_writer_unlock - inc reader count & spin until writer is gone
  * @lock  : Pointer to queue rwlock structure
@@ -127,7 +124,8 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
                struct __qrwlock *l = (struct __qrwlock *)lock;
 
                if (!READ_ONCE(l->wmode) &&
-                  (cmpxchg_relaxed(&l->wmode, 0, _QW_WAITING) == 0))
+                  (cmpxchg_relaxed(&l->wmode, 0,
+                                       _QW_MODEVAL(_QW_WAITING)) == 0))
                        break;
 
                cpu_relax_lowlatency();
-- 
1.9.1