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-rw-r--r--lib/dec_and_lock.c35
1 files changed, 35 insertions, 0 deletions
diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c
index 2377af057d09..305a9663aee3 100644
--- a/lib/dec_and_lock.c
+++ b/lib/dec_and_lock.c
@@ -1,7 +1,41 @@
1#include <linux/module.h> 1#include <linux/module.h>
2#include <linux/spinlock.h> 2#include <linux/spinlock.h>
3#include <asm/atomic.h> 3#include <asm/atomic.h>
4#include <asm/system.h>
4 5
6#ifdef __HAVE_ARCH_CMPXCHG
7/*
8 * This is an implementation of the notion of "decrement a
9 * reference count, and return locked if it decremented to zero".
10 *
11 * This implementation can be used on any architecture that
12 * has a cmpxchg, and where atomic->value is an int holding
13 * the value of the atomic (i.e. the high bits aren't used
14 * for a lock or anything like that).
15 */
16int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
17{
18 int counter;
19 int newcount;
20
21 for (;;) {
22 counter = atomic_read(atomic);
23 newcount = counter - 1;
24 if (!newcount)
25 break; /* do it the slow way */
26
27 newcount = cmpxchg(&atomic->counter, counter, newcount);
28 if (newcount == counter)
29 return 0;
30 }
31
32 spin_lock(lock);
33 if (atomic_dec_and_test(atomic))
34 return 1;
35 spin_unlock(lock);
36 return 0;
37}
38#else
5/* 39/*
6 * This is an architecture-neutral, but slow, 40 * This is an architecture-neutral, but slow,
7 * implementation of the notion of "decrement 41 * implementation of the notion of "decrement
@@ -33,5 +67,6 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
33 spin_unlock(lock); 67 spin_unlock(lock);
34 return 0; 68 return 0;
35} 69}
70#endif
36 71
37EXPORT_SYMBOL(_atomic_dec_and_lock); 72EXPORT_SYMBOL(_atomic_dec_and_lock);