forked from mirrors/linux
360f54796e
We can be more aggressive about this, if we are clever and careful. This is subtle. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
51 lines
1.4 KiB
C
51 lines
1.4 KiB
C
#ifndef __LINUX_LOCKREF_H
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#define __LINUX_LOCKREF_H
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/*
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* Locked reference counts.
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*
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* These are different from just plain atomic refcounts in that they
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* are atomic with respect to the spinlock that goes with them. In
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* particular, there can be implementations that don't actually get
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* the spinlock for the common decrement/increment operations, but they
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* still have to check that the operation is done semantically as if
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* the spinlock had been taken (using a cmpxchg operation that covers
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* both the lock and the count word, or using memory transactions, for
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* example).
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*/
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#include <linux/spinlock.h>
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#include <generated/bounds.h>
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#define USE_CMPXCHG_LOCKREF \
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(IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \
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IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4)
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struct lockref {
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union {
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#if USE_CMPXCHG_LOCKREF
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aligned_u64 lock_count;
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#endif
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struct {
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spinlock_t lock;
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int count;
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};
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};
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};
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extern void lockref_get(struct lockref *);
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extern int lockref_put_return(struct lockref *);
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extern int lockref_get_not_zero(struct lockref *);
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extern int lockref_get_or_lock(struct lockref *);
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extern int lockref_put_or_lock(struct lockref *);
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extern void lockref_mark_dead(struct lockref *);
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extern int lockref_get_not_dead(struct lockref *);
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/* Must be called under spinlock for reliable results */
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static inline int __lockref_is_dead(const struct lockref *l)
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{
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return ((int)l->count < 0);
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}
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#endif /* __LINUX_LOCKREF_H */
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