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https://github.com/torvalds/linux
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68573b936d
Use try_cmpxchg() family of functions instead of cmpxchg (*ptr, old, new) == old. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. No functional change intended. Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Kent Overstreet <kent.overstreet@linux.dev> Cc: Brian Foster <bfoster@redhat.com> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
59 lines
1.3 KiB
C
59 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _BCACHEFS_TWO_STATE_LOCK_H
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#define _BCACHEFS_TWO_STATE_LOCK_H
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#include <linux/atomic.h>
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#include <linux/sched.h>
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#include <linux/wait.h>
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#include "util.h"
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/*
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* Two-state lock - can be taken for add or block - both states are shared,
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* like read side of rwsem, but conflict with other state:
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*/
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typedef struct {
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atomic_long_t v;
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wait_queue_head_t wait;
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} two_state_lock_t;
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static inline void two_state_lock_init(two_state_lock_t *lock)
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{
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atomic_long_set(&lock->v, 0);
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init_waitqueue_head(&lock->wait);
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}
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static inline void bch2_two_state_unlock(two_state_lock_t *lock, int s)
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{
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long i = s ? 1 : -1;
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EBUG_ON(atomic_long_read(&lock->v) == 0);
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if (atomic_long_sub_return_release(i, &lock->v) == 0)
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wake_up_all(&lock->wait);
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}
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static inline bool bch2_two_state_trylock(two_state_lock_t *lock, int s)
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{
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long i = s ? 1 : -1;
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long old;
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old = atomic_long_read(&lock->v);
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do {
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if (i > 0 ? old < 0 : old > 0)
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return false;
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} while (!atomic_long_try_cmpxchg_acquire(&lock->v, &old, old + i));
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return true;
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}
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void __bch2_two_state_lock(two_state_lock_t *, int);
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static inline void bch2_two_state_lock(two_state_lock_t *lock, int s)
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{
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if (!bch2_two_state_trylock(lock, s))
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__bch2_two_state_lock(lock, s);
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}
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#endif /* _BCACHEFS_TWO_STATE_LOCK_H */
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