Linux-2.6.12-rc2
[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 <asm/atomic.h>
12
13 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
14 {
15         int counter;
16         int newcount;
17
18 repeat:
19         counter = atomic_read(atomic);
20         newcount = counter-1;
21
22         if (!newcount)
23                 goto slow_path;
24
25         asm volatile("lock; cmpxchgl %1,%2"
26                 :"=a" (newcount)
27                 :"r" (newcount), "m" (atomic->counter), "0" (counter));
28
29         /* If the above failed, "eax" will have changed */
30         if (newcount != counter)
31                 goto repeat;
32         return 0;
33
34 slow_path:
35         spin_lock(lock);
36         if (atomic_dec_and_test(atomic))
37                 return 1;
38         spin_unlock(lock);
39         return 0;
40 }