Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / lib / dec_and_lock.c
bloba65c314555416d9f1ea262455d1da313e1959902
1 #include <linux/module.h>
2 #include <linux/spinlock.h>
3 #include <asm/atomic.h>
5 /*
6 * This is an implementation of the notion of "decrement a
7 * reference count, and return locked if it decremented to zero".
9 * NOTE NOTE NOTE! This is _not_ equivalent to
11 * if (atomic_dec_and_test(&atomic)) {
12 * spin_lock(&lock);
13 * return 1;
14 * }
15 * return 0;
17 * because the spin-lock and the decrement must be
18 * "atomic".
20 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
22 #ifdef CONFIG_SMP
23 /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
24 if (atomic_add_unless(atomic, -1, 1))
25 return 0;
26 #endif
27 /* Otherwise do it the slow way */
28 spin_lock(lock);
29 if (atomic_dec_and_test(atomic))
30 return 1;
31 spin_unlock(lock);
32 return 0;
35 EXPORT_SYMBOL(_atomic_dec_and_lock);