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-rw-r--r--arch/i386/lib/dec_and_lock.c40
1 files changed, 40 insertions, 0 deletions
diff --git a/arch/i386/lib/dec_and_lock.c b/arch/i386/lib/dec_and_lock.c
new file mode 100644
index 00000000000..ab43394dc77
--- /dev/null
+++ b/arch/i386/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;
+}