On 06/15/2016 05:31 AM, Pan Xinhui wrote:
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.deacon@xxxxxxx>
Signed-off-by: Pan Xinhui<xinhui.pan@xxxxxxxxxxxxxxxxxx>
---
change from v1:
A typo fix which is really bad...
thanks Will for the carefull review. :)
---
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..28fb94a 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_SHIFT 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)
I know what you are doing here, but it is a bit hard to understand it
just by looking at the name of the macro itself. Maybe some other names
like _QW_MASKVAL() or_QW_BYTEVAL(). You may also want to have a line of
comment about it. Other than that, I don't see any problem with it.
Acked-by: Waiman Long <Waiman.Long@xxxxxxx>
+
/**
* 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();
--
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