[LIB]: Consolidate _atomic_dec_and_lock()

Several implementations were essentialy a common piece of C code using
the cmpxchg() macro.  Put the implementation in one spot that everyone
can share, and convert sparc64 over to using this.

Alpha is the lone arch-specific implementation, which codes up a
special fast path for the common case in order to avoid GP reloading
which a pure C version would require.

Signed-off-by: David S. Miller <davem@davemloft.net>

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 @@
 #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
@@ -33,5 +67,6 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
         spin_unlock(lock);
         return 0;
 }
+#endif
 
 EXPORT_SYMBOL(_atomic_dec_and_lock);