diff options
Diffstat (limited to 'include/asm-generic/qrwlock.h')
| -rw-r--r-- | include/asm-generic/qrwlock.h | 126 |
1 files changed, 46 insertions, 80 deletions
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h index 7d026bf27713..75b8f4601b28 100644 --- a/include/asm-generic/qrwlock.h +++ b/include/asm-generic/qrwlock.h @@ -1,15 +1,10 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ /* * Queue read/write lock * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. + * These use generic atomic and locking routines, but depend on a fair spinlock + * implementation in order to be fair themselves. The implementation in + * asm-generic/spinlock.h meets these requirements. * * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. * @@ -24,60 +19,31 @@ #include <asm-generic/qrwlock_types.h> +/* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */ + /* * Writer states & reader shift and bias. - * - * | +0 | +1 | +2 | +3 | - * ----+----+----+----+----+ - * LE | 78 | 56 | 34 | 12 | 0x12345678 - * ----+----+----+----+----+ - * | wr | rd | - * +----+----+----+----+ - * - * ----+----+----+----+----+ - * BE | 12 | 34 | 56 | 78 | 0x12345678 - * ----+----+----+----+----+ - * | rd | wr | - * +----+----+----+----+ */ -#define _QW_WAITING 1 /* A writer is waiting */ -#define _QW_LOCKED 0xff /* A writer holds the lock */ -#define _QW_WMASK 0xff /* Writer mask */ -#define _QR_SHIFT 8 /* Reader count shift */ +#define _QW_WAITING 0x100 /* A writer is waiting */ +#define _QW_LOCKED 0x0ff /* A writer holds the lock */ +#define _QW_WMASK 0x1ff /* Writer mask */ +#define _QR_SHIFT 9 /* Reader count shift */ #define _QR_BIAS (1U << _QR_SHIFT) /* * External function declarations */ -extern void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts); +extern void queued_read_lock_slowpath(struct qrwlock *lock); extern void queued_write_lock_slowpath(struct qrwlock *lock); /** - * queued_read_can_lock- would read_trylock() succeed? - * @lock: Pointer to queue rwlock structure - */ -static inline int queued_read_can_lock(struct qrwlock *lock) -{ - return !(atomic_read(&lock->cnts) & _QW_WMASK); -} - -/** - * queued_write_can_lock- would write_trylock() succeed? - * @lock: Pointer to queue rwlock structure - */ -static inline int queued_write_can_lock(struct qrwlock *lock) -{ - return !atomic_read(&lock->cnts); -} - -/** - * queued_read_trylock - try to acquire read lock of a queue rwlock - * @lock : Pointer to queue rwlock structure + * queued_read_trylock - try to acquire read lock of a queued rwlock + * @lock : Pointer to queued rwlock structure * Return: 1 if lock acquired, 0 if failed */ static inline int queued_read_trylock(struct qrwlock *lock) { - u32 cnts; + int cnts; cnts = atomic_read(&lock->cnts); if (likely(!(cnts & _QW_WMASK))) { @@ -90,53 +56,54 @@ static inline int queued_read_trylock(struct qrwlock *lock) } /** - * queued_write_trylock - try to acquire write lock of a queue rwlock - * @lock : Pointer to queue rwlock structure + * queued_write_trylock - try to acquire write lock of a queued rwlock + * @lock : Pointer to queued rwlock structure * Return: 1 if lock acquired, 0 if failed */ static inline int queued_write_trylock(struct qrwlock *lock) { - u32 cnts; + int cnts; cnts = atomic_read(&lock->cnts); if (unlikely(cnts)) return 0; - return likely(atomic_cmpxchg_acquire(&lock->cnts, - cnts, cnts | _QW_LOCKED) == cnts); + return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, + _QW_LOCKED)); } /** - * queued_read_lock - acquire read lock of a queue rwlock - * @lock: Pointer to queue rwlock structure + * queued_read_lock - acquire read lock of a queued rwlock + * @lock: Pointer to queued rwlock structure */ static inline void queued_read_lock(struct qrwlock *lock) { - u32 cnts; + int cnts; cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts); if (likely(!(cnts & _QW_WMASK))) return; /* The slowpath will decrement the reader count, if necessary. */ - queued_read_lock_slowpath(lock, cnts); + queued_read_lock_slowpath(lock); } /** - * queued_write_lock - acquire write lock of a queue rwlock - * @lock : Pointer to queue rwlock structure + * queued_write_lock - acquire write lock of a queued rwlock + * @lock : Pointer to queued rwlock structure */ static inline void queued_write_lock(struct qrwlock *lock) { + int cnts = 0; /* Optimize for the unfair lock case where the fair flag is 0. */ - if (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0) + if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))) return; queued_write_lock_slowpath(lock); } /** - * queued_read_unlock - release read lock of a queue rwlock - * @lock : Pointer to queue rwlock structure + * queued_read_unlock - release read lock of a queued rwlock + * @lock : Pointer to queued rwlock structure */ static inline void queued_read_unlock(struct qrwlock *lock) { @@ -147,35 +114,34 @@ static inline void queued_read_unlock(struct qrwlock *lock) } /** - * __qrwlock_write_byte - retrieve the write byte address of a queue rwlock - * @lock : Pointer to queue rwlock structure - * Return: the write byte address of a queue rwlock + * queued_write_unlock - release write lock of a queued rwlock + * @lock : Pointer to queued rwlock structure */ -static inline u8 *__qrwlock_write_byte(struct qrwlock *lock) +static inline void queued_write_unlock(struct qrwlock *lock) { - return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN); + smp_store_release(&lock->wlocked, 0); } /** - * queued_write_unlock - release write lock of a queue rwlock - * @lock : Pointer to queue rwlock structure + * queued_rwlock_is_contended - check if the lock is contended + * @lock : Pointer to queued rwlock structure + * Return: 1 if lock contended, 0 otherwise */ -static inline void queued_write_unlock(struct qrwlock *lock) +static inline int queued_rwlock_is_contended(struct qrwlock *lock) { - smp_store_release(__qrwlock_write_byte(lock), 0); + return arch_spin_is_locked(&lock->wait_lock); } /* * Remapping rwlock architecture specific functions to the corresponding - * queue rwlock functions. + * queued rwlock functions. */ -#define arch_read_can_lock(l) queued_read_can_lock(l) -#define arch_write_can_lock(l) queued_write_can_lock(l) -#define arch_read_lock(l) queued_read_lock(l) -#define arch_write_lock(l) queued_write_lock(l) -#define arch_read_trylock(l) queued_read_trylock(l) -#define arch_write_trylock(l) queued_write_trylock(l) -#define arch_read_unlock(l) queued_read_unlock(l) -#define arch_write_unlock(l) queued_write_unlock(l) +#define arch_read_lock(l) queued_read_lock(l) +#define arch_write_lock(l) queued_write_lock(l) +#define arch_read_trylock(l) queued_read_trylock(l) +#define arch_write_trylock(l) queued_write_trylock(l) +#define arch_read_unlock(l) queued_read_unlock(l) +#define arch_write_unlock(l) queued_write_unlock(l) +#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l) #endif /* __ASM_GENERIC_QRWLOCK_H */ |