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authorNick Piggin <nickpiggin@yahoo.com.au>2006-01-08 01:02:19 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-01-08 20:13:48 -0800
commita57004e1afb6ee03c509f1b1ec74a000682ab93b (patch)
tree846112d14bc2ea20ebaf069c83909485fc91655c /lib/dec_and_lock.c
parent8382bf2e72d16d0532e351299121ccd3bca0fdd8 (diff)
downloadlinux-sh-a57004e1afb6ee03c509f1b1ec74a000682ab93b.tar.gz
[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 @@
#include <linux/module.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
-#include <asm/system.h>
-#ifdef __HAVE_ARCH_CMPXCHG
/*
* This is an implementation of the notion of "decrement a
* reference count, and return locked if it decremented to zero".
*
- * This implementation can be used on any architecture that
- * has a cmpxchg, and where atomic->value is an int holding
- * the value of the atomic (i.e. the high bits aren't used
- * for a lock or anything like that).
- */
-int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
-{
- int counter;
- int newcount;
-
- for (;;) {
- counter = atomic_read(atomic);
- newcount = counter - 1;
- if (!newcount)
- break; /* do it the slow way */
-
- newcount = cmpxchg(&atomic->counter, counter, newcount);
- if (newcount == counter)
- return 0;
- }
-
- spin_lock(lock);
- if (atomic_dec_and_test(atomic))
- return 1;
- spin_unlock(lock);
- return 0;
-}
-#else
-/*
- * This is an architecture-neutral, but slow,
- * implementation of the notion of "decrement
- * a reference count, and return locked if it
- * decremented to zero".
- *
* NOTE NOTE NOTE! This is _not_ equivalent to
*
* if (atomic_dec_and_test(&atomic)) {
@@ -52,21 +16,20 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
*
* because the spin-lock and the decrement must be
* "atomic".
- *
- * This slow version gets the spinlock unconditionally,
- * and releases it if it isn't needed. Architectures
- * are encouraged to come up with better approaches,
- * this is trivially done efficiently using a load-locked
- * store-conditional approach, for example.
*/
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{
+#ifdef CONFIG_SMP
+ /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
+ if (atomic_add_unless(atomic, -1, 1))
+ return 0;
+#endif
+ /* Otherwise do it the slow way */
spin_lock(lock);
if (atomic_dec_and_test(atomic))
return 1;
spin_unlock(lock);
return 0;
}
-#endif
EXPORT_SYMBOL(_atomic_dec_and_lock);