Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * MIPS version of atomic_dec_and_lock() using cmpxchg |
| 3 | * |
| 4 | * This program is free software; you can redistribute it and/or |
| 5 | * modify it under the terms of the GNU General Public License |
| 6 | * as published by the Free Software Foundation; either version |
| 7 | * 2 of the License, or (at your option) any later version. |
| 8 | */ |
| 9 | |
| 10 | #include <linux/module.h> |
| 11 | #include <linux/spinlock.h> |
| 12 | #include <asm/atomic.h> |
| 13 | #include <asm/system.h> |
| 14 | |
| 15 | /* |
| 16 | * This is an implementation of the notion of "decrement a |
| 17 | * reference count, and return locked if it decremented to zero". |
| 18 | * |
| 19 | * This implementation can be used on any architecture that |
| 20 | * has a cmpxchg, and where atomic->value is an int holding |
| 21 | * the value of the atomic (i.e. the high bits aren't used |
| 22 | * for a lock or anything like that). |
| 23 | * |
| 24 | * N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h |
| 25 | * if spinlocks are empty and thus atomic_dec_and_lock is defined |
| 26 | * to be atomic_dec_and_test - in that case we don't need it |
| 27 | * defined here as well. |
| 28 | */ |
| 29 | |
| 30 | #ifndef ATOMIC_DEC_AND_LOCK |
| 31 | int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) |
| 32 | { |
| 33 | int counter; |
| 34 | int newcount; |
| 35 | |
| 36 | for (;;) { |
| 37 | counter = atomic_read(atomic); |
| 38 | newcount = counter - 1; |
| 39 | if (!newcount) |
| 40 | break; /* do it the slow way */ |
| 41 | |
| 42 | newcount = cmpxchg(&atomic->counter, counter, newcount); |
| 43 | if (newcount == counter) |
| 44 | return 0; |
| 45 | } |
| 46 | |
| 47 | spin_lock(lock); |
| 48 | if (atomic_dec_and_test(atomic)) |
| 49 | return 1; |
| 50 | spin_unlock(lock); |
| 51 | return 0; |
| 52 | } |
| 53 | |
| 54 | EXPORT_SYMBOL(_atomic_dec_and_lock); |
| 55 | #endif /* ATOMIC_DEC_AND_LOCK */ |