This patch modifies the queue_write_unlock() function to use the new
smp_store_release() function (currently in tip). It also removes the
temporary implementation of smp_load_acquire() and smp_store_release()
function in qrwlock.c.
This patch will use atomic subtraction instead if the writer field is
not atomic.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
---
include/asm-generic/qrwlock.h | 10 ++++++----
kernel/locking/qrwlock.c | 34 ----------------------------------
2 files changed, 6 insertions(+), 38 deletions(-)
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 5abb6ca..68f488b 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -181,11 +181,13 @@ static inline void queue_read_unlock(struct qrwlock *lock)
static inline void queue_write_unlock(struct qrwlock *lock)
{
/*
- * Make sure that none of the critical section will be leaked out.
+ * If the writer field is atomic, it can be cleared directly.
+ * Otherwise, an atomic subtraction will be used to clear it.
*/
- smp_mb__before_clear_bit();
- ACCESS_ONCE(lock->cnts.writer) = 0;
- smp_mb__after_clear_bit();
+ if (__native_word(lock->cnts.writer))
+ smp_store_release(&lock->cnts.writer, 0);
+ else
+ atomic_sub(_QW_LOCKED, &lock->cnts.rwa);
}
/*
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index 053be4d..2727188 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -47,40 +47,6 @@
# define arch_mutex_cpu_relax() cpu_relax()
#endif
-#ifndef smp_load_acquire
-# ifdef CONFIG_X86
-# define smp_load_acquire(p) \
- ({ \
- typeof(*p) ___p1 = ACCESS_ONCE(*p); \
- barrier(); \
- ___p1; \
- })
-# else
-# define smp_load_acquire(p) \
- ({ \
- typeof(*p) ___p1 = ACCESS_ONCE(*p); \
- smp_mb(); \
- ___p1; \
- })
-# endif
-#endif
-
-#ifndef smp_store_release
-# ifdef CONFIG_X86
-# define smp_store_release(p, v) \
- do { \
- barrier(); \
- ACCESS_ONCE(*p) = v; \
- } while (0)
-# else
-# define smp_store_release(p, v) \
- do { \
- smp_mb(); \
- ACCESS_ONCE(*p) = v; \
- } while (0)
-# endif
-#endif
-
/*
* If an xadd (exchange-add) macro isn't available, simulate one with
* the atomic_add_return() function.
--
1.7.1
--
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