diff options
Diffstat (limited to 'lib/dec_and_lock.c')
| -rw-r--r-- | lib/dec_and_lock.c | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c index 2377af0..305a966 100644 --- a/lib/dec_and_lock.c +++ b/lib/dec_and_lock.c @@ -1,7 +1,41 @@ #include <linux/module.h> #include <linux/spinlock.h> #include <asm/atomic.h> +#include <asm/system.h> +#ifdef __HAVE_ARCH_CMPXCHG +/* + * This is an implementation of the notion of "decrement a + * reference count, and return locked if it decremented to zero". + * + * This implementation can be used on any architecture that + * has a cmpxchg, and where atomic->value is an int holding + * the value of the atomic (i.e. the high bits aren't used + * for a lock or anything like that). + */ +int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) +{ + int counter; + int newcount; + + for (;;) { + counter = atomic_read(atomic); + newcount = counter - 1; + if (!newcount) + break; /* do it the slow way */ + + newcount = cmpxchg(&atomic->counter, counter, newcount); + if (newcount == counter) + return 0; + } + + spin_lock(lock); + if (atomic_dec_and_test(atomic)) + return 1; + spin_unlock(lock); + return 0; +} +#else /* * This is an architecture-neutral, but slow, * implementation of the notion of "decrement @@ -33,5 +67,6 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) spin_unlock(lock); return 0; } +#endif EXPORT_SYMBOL(_atomic_dec_and_lock); |