patch-2.4.20 linux-2.4.20/arch/x86_64/lib/dec_and_lock.c

• Lines: 41
• Date: Thu Nov 28 15:53:12 2002
• Orig file: linux-2.4.19/arch/x86_64/lib/dec_and_lock.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -urN linux-2.4.19/arch/x86_64/lib/dec_and_lock.c linux-2.4.20/arch/x86_64/lib/dec_and_lock.c
@@ -0,0 +1,40 @@
+/*
+ * x86 version of "atomic_dec_and_lock()" using
+ * the atomic "cmpxchg" instruction.
+ *
+ * (For CPU's lacking cmpxchg, we use the slow
+ * generic version, and this one never even gets
+ * compiled).
+ */
+
+#include <linux/spinlock.h>
+#include <asm/atomic.h>
+
+int atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
+{
+	int counter;
+	int newcount;
+
+repeat:
+	counter = atomic_read(atomic);
+	newcount = counter-1;
+
+	if (!newcount)
+		goto slow_path;
+
+	asm volatile("lock; cmpxchgl %1,%2"
+		:"=a" (newcount)
+		:"r" (newcount), "m" (atomic->counter), "0" (counter));
+
+	/* If the above failed, "eax" will have changed */
+	if (newcount != counter)
+		goto repeat;
+	return 0;
+
+slow_path:
+	spin_lock(lock);
+	if (atomic_dec_and_test(atomic))
+		return 1;
+	spin_unlock(lock);
+	return 0;
+}