diff options
Diffstat (limited to 'include/linux/lockref.h')
| -rw-r--r-- | include/linux/lockref.h | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/include/linux/lockref.h b/include/linux/lockref.h new file mode 100644 index 000000000..c3a1f78bc --- /dev/null +++ b/include/linux/lockref.h @@ -0,0 +1,52 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __LINUX_LOCKREF_H +#define __LINUX_LOCKREF_H + +/* + * Locked reference counts. + * + * These are different from just plain atomic refcounts in that they + * are atomic with respect to the spinlock that goes with them. In + * particular, there can be implementations that don't actually get + * the spinlock for the common decrement/increment operations, but they + * still have to check that the operation is done semantically as if + * the spinlock had been taken (using a cmpxchg operation that covers + * both the lock and the count word, or using memory transactions, for + * example). + */ + +#include <linux/spinlock.h> +#include <generated/bounds.h> + +#define USE_CMPXCHG_LOCKREF \ + (IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \ + IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4) + +struct lockref { + union { +#if USE_CMPXCHG_LOCKREF + aligned_u64 lock_count; +#endif + struct { + spinlock_t lock; + int count; + }; + }; +}; + +extern void lockref_get(struct lockref *); +extern int lockref_put_return(struct lockref *); +extern int lockref_get_not_zero(struct lockref *); +extern int lockref_put_not_zero(struct lockref *); +extern int lockref_put_or_lock(struct lockref *); + +extern void lockref_mark_dead(struct lockref *); +extern int lockref_get_not_dead(struct lockref *); + +/* Must be called under spinlock for reliable results */ +static inline bool __lockref_is_dead(const struct lockref *l) +{ + return ((int)l->count < 0); +} + +#endif /* __LINUX_LOCKREF_H */ |