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authorNick Piggin <nickpiggin@yahoo.com.au>2006-01-08 04:02:19 -0500
committerLinus Torvalds <torvalds@g5.osdl.org>2006-01-08 23:13:48 -0500
commita57004e1afb6ee03c509f1b1ec74a000682ab93b (patch)
tree846112d14bc2ea20ebaf069c83909485fc91655c /lib/dec_and_lock.c
parent8382bf2e72d16d0532e351299121ccd3bca0fdd8 (diff)
[PATCH] atomic: dec_and_lock use atomic primitives
Convert atomic_dec_and_lock to use new atomic primitives. Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: "Paul E. McKenney" <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'lib/dec_and_lock.c')
-rw-r--r--lib/dec_and_lock.c49
1 files changed, 6 insertions, 43 deletions
diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c
index 305a9663aee3..a65c31455541 100644
--- a/lib/dec_and_lock.c
+++ b/lib/dec_and_lock.c
@@ -1,47 +1,11 @@
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>
5 4
6#ifdef __HAVE_ARCH_CMPXCHG
7/* 5/*
8 * This is an implementation of the notion of "decrement a 6 * This is an implementation of the notion of "decrement a
9 * reference count, and return locked if it decremented to zero". 7 * reference count, and return locked if it decremented to zero".
10 * 8 *
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
39/*
40 * This is an architecture-neutral, but slow,
41 * implementation of the notion of "decrement
42 * a reference count, and return locked if it
43 * decremented to zero".
44 *
45 * NOTE NOTE NOTE! This is _not_ equivalent to 9 * NOTE NOTE NOTE! This is _not_ equivalent to
46 * 10 *
47 * if (atomic_dec_and_test(&atomic)) { 11 * if (atomic_dec_and_test(&atomic)) {
@@ -52,21 +16,20 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
52 * 16 *
53 * because the spin-lock and the decrement must be 17 * because the spin-lock and the decrement must be
54 * "atomic". 18 * "atomic".
55 *
56 * This slow version gets the spinlock unconditionally,
57 * and releases it if it isn't needed. Architectures
58 * are encouraged to come up with better approaches,
59 * this is trivially done efficiently using a load-locked
60 * store-conditional approach, for example.
61 */ 19 */
62int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) 20int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
63{ 21{
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 */
64 spin_lock(lock); 28 spin_lock(lock);
65 if (atomic_dec_and_test(atomic)) 29 if (atomic_dec_and_test(atomic))
66 return 1; 30 return 1;
67 spin_unlock(lock); 31 spin_unlock(lock);
68 return 0; 32 return 0;
69} 33}
70#endif
71 34
72EXPORT_SYMBOL(_atomic_dec_and_lock); 35EXPORT_SYMBOL(_atomic_dec_and_lock);