From 84c6591103dbeaf393a092a3fc7b09510825f6b9 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 19 Jun 2018 13:53:12 +0100 Subject: [PATCH] locking/atomics, asm-generic/bitops/lock.h: Rewrite using atomic_fetch_*() 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. Signed-off-by: Will Deacon Acked-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-arm-kernel@lists.infradead.org Cc: yamada.masahiro@socionext.com Link: https://lore.kernel.org/lkml/1529412794-17720-8-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar --- 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 67ab280ad13401..3ae021368f4854 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 +#include +#include + /** * 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_ */