Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | #include <linux/module.h> |
| 2 | #include <linux/spinlock.h> |
| 3 | #include <asm/atomic.h> |
| 4 | #include <asm/system.h> |
| 5 | |
| 6 | /* |
| 7 | * This is an implementation of the notion of "decrement a |
| 8 | * reference count, and return locked if it decremented to zero". |
| 9 | * |
| 10 | * This implementation can be used on any architecture that |
| 11 | * has a cmpxchg, and where atomic->value is an int holding |
| 12 | * the value of the atomic (i.e. the high bits aren't used |
| 13 | * for a lock or anything like that). |
| 14 | * |
| 15 | * N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h |
| 16 | * if spinlocks are empty and thus atomic_dec_and_lock is defined |
| 17 | * to be atomic_dec_and_test - in that case we don't need it |
| 18 | * defined here as well. |
| 19 | */ |
| 20 | |
| 21 | #ifndef ATOMIC_DEC_AND_LOCK |
| 22 | int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) |
| 23 | { |
| 24 | int counter; |
| 25 | int newcount; |
| 26 | |
| 27 | for (;;) { |
| 28 | counter = atomic_read(atomic); |
| 29 | newcount = counter - 1; |
| 30 | if (!newcount) |
| 31 | break; /* do it the slow way */ |
| 32 | |
| 33 | newcount = cmpxchg(&atomic->counter, counter, newcount); |
| 34 | if (newcount == counter) |
| 35 | return 0; |
| 36 | } |
| 37 | |
| 38 | spin_lock(lock); |
| 39 | if (atomic_dec_and_test(atomic)) |
| 40 | return 1; |
| 41 | spin_unlock(lock); |
| 42 | return 0; |
| 43 | } |
| 44 | |
| 45 | EXPORT_SYMBOL(_atomic_dec_and_lock); |
| 46 | #endif /* ATOMIC_DEC_AND_LOCK */ |