The lock bitops can be implemented more efficiently using the atomic_fetch_*
ops, which provide finer-grained control over the memory ordering semantics
than the bitops.
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Will Deacon <will.dea...@arm.com>
---
include/asm-generic/bitops/lock.h | 68 ++++++++++++++++++++++++++++++++-------
1 file changed, 56 insertions(+), 12 deletions(-)
diff --git a/include/asm-generic/bitops/lock.h
b/include/asm-generic/bitops/lock.h
index 67ab280ad134..3ae021368f48 100644
--- a/include/asm-generic/bitops/lock.h
+++ b/include/asm-generic/bitops/lock.h
@@ -2,6 +2,10 @@
#ifndef _ASM_GENERIC_BITOPS_LOCK_H_
#define _ASM_GENERIC_BITOPS_LOCK_H_
+#include <linux/atomic.h>
+#include <linux/compiler.h>
+#include <asm/barrier.h>
+
/**
* test_and_set_bit_lock - Set a bit and return its old value, for lock
* @nr: Bit to set
@@ -11,7 +15,20 @@
* the returned value is 0.
* It can be used to implement bit locks.
*/
-#define test_and_set_bit_lock(nr, addr) test_and_set_bit(nr, addr)
+static inline int test_and_set_bit_lock(unsigned int nr,
+ volatile unsigned long *p)
+{
+ long old;
+ unsigned long mask = BIT_MASK(nr);
+
+ p += BIT_WORD(nr);
+ if (READ_ONCE(*p) & mask)
+ return 1;
+
+ old = atomic_long_fetch_or_acquire(mask, (atomic_long_t *)p);
+ return !!(old & mask);
+}
+
/**
* clear_bit_unlock - Clear a bit in memory, for unlock
@@ -20,11 +37,11 @@
*
* This operation is atomic and provides release barrier semantics.
*/
-#define clear_bit_unlock(nr, addr) \
-do { \
- smp_mb__before_atomic(); \
- clear_bit(nr, addr); \
-} while (0)
+static inline void clear_bit_unlock(unsigned int nr, volatile unsigned long *p)
+{
+ p += BIT_WORD(nr);
+ atomic_long_fetch_andnot_release(BIT_MASK(nr), (atomic_long_t *)p);
+}
/**
* __clear_bit_unlock - Clear a bit in memory, for unlock
@@ -37,11 +54,38 @@ do { \
*
* See for example x86's implementation.
*/
-#define __clear_bit_unlock(nr, addr) \
-do { \
- smp_mb__before_atomic(); \
- clear_bit(nr, addr); \
-} while (0)
+static inline void __clear_bit_unlock(unsigned int nr,
+ volatile unsigned long *p)
+{
+ unsigned long old;
-#endif /* _ASM_GENERIC_BITOPS_LOCK_H_ */
+ p += BIT_WORD(nr);
+ old = READ_ONCE(*p);
+ old &= ~BIT_MASK(nr);
+ atomic_long_set_release((atomic_long_t *)p, old);
+}
+
+/**
+ * clear_bit_unlock_is_negative_byte - Clear a bit in memory and test if bottom
+ * byte is negative, for unlock.
+ * @nr: the bit to clear
+ * @addr: the address to start counting from
+ *
+ * This is a bit of a one-trick-pony for the filemap code, which clears
+ * PG_locked and tests PG_waiters,
+ */
+#ifndef clear_bit_unlock_is_negative_byte
+static inline bool clear_bit_unlock_is_negative_byte(unsigned int nr,
+ volatile unsigned long *p)
+{
+ long old;
+ unsigned long mask = BIT_MASK(nr);
+
+ p += BIT_WORD(nr);
+ old = atomic_long_fetch_andnot_release(mask, (atomic_long_t *)p);
+ return !!(old & BIT(7));
+}
+#define clear_bit_unlock_is_negative_byte clear_bit_unlock_is_negative_byte
+#endif
+#endif /* _ASM_GENERIC_BITOPS_LOCK_H_ */
--
2.1.4
