kbuild: full dependency check on asm-offsets.h
[linux-2.6.git] / arch / i386 / lib / dec_and_lock.c
1 /*
2  * x86 version of "atomic_dec_and_lock()" using
3  * the atomic "cmpxchg" instruction.
4  *
5  * (For CPU's lacking cmpxchg, we use the slow
6  * generic version, and this one never even gets
7  * compiled).
8  */
9
10 #include <linux/spinlock.h>
11 #include <linux/module.h>
12 #include <asm/atomic.h>
13
14 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
15 {
16         int counter;
17         int newcount;
18
19 repeat:
20         counter = atomic_read(atomic);
21         newcount = counter-1;
22
23         if (!newcount)
24                 goto slow_path;
25
26         asm volatile("lock; cmpxchgl %1,%2"
27                 :"=a" (newcount)
28                 :"r" (newcount), "m" (atomic->counter), "0" (counter));
29
30         /* If the above failed, "eax" will have changed */
31         if (newcount != counter)
32                 goto repeat;
33         return 0;
34
35 slow_path:
36         spin_lock(lock);
37         if (atomic_dec_and_test(atomic))
38                 return 1;
39         spin_unlock(lock);
40         return 0;
41 }
42 EXPORT_SYMBOL(_atomic_dec_and_lock);