1 files changed, 84 insertions, 0 deletions
diff --git a/c_src/include/linux/bit_spinlock.h b/c_src/include/linux/bit_spinlock.h
new file mode 100644
index 00000000..873f08c2
--- /dev/null
+++ b/c_src/include/linux/bit_spinlock.h
@@ -0,0 +1,84 @@
+#ifndef __LINUX_BIT_SPINLOCK_H
+#define __LINUX_BIT_SPINLOCK_H
+
+#include <linux/kernel.h>
+#include <linux/preempt.h>
+#include <linux/futex.h>
+#include <urcu/futex.h>
+
+/*
+ * The futex wait op wants an explicit 32-bit address and value. If the bitmap
+ * used for the spinlock is 64-bit, cast down and pass the right 32-bit region
+ * for the in-kernel checks. The value is the copy that has already been read
+ * from the atomic op.
+ *
+ * The futex wake op interprets the value as the number of waiters to wake (up
+ * to INT_MAX), so pass that along directly.
+ */
+static inline void do_futex(int nr, unsigned long *addr, unsigned long v, int futex_flags)
+{
+	u32 *addr32 = (u32 *) addr;
+	u32 *v32 = (u32 *) &v;
+	int shift = 0;
+
+	futex_flags |= FUTEX_PRIVATE_FLAG;
+
+#if BITS_PER_LONG == 64
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	shift = (nr >= 32) ? 1 : 0;
+#else
+	shift = (nr < 32) ? 1 : 0;
+#endif
+#endif
+	if (shift) {
+		addr32 += shift;
+		v32 += shift;
+	}
+	/*
+	 * The shift to determine the futex address may have cast away a
+	 * literal wake count value. The value is capped to INT_MAX and thus
+	 * always in the low bytes of v regardless of bit nr. Copy in the wake
+	 * count to whatever 32-bit range was selected.
+	 */
+	if (futex_flags == FUTEX_WAKE_PRIVATE)
+		*v32 = (u32) v;
+	futex(addr32, futex_flags, *v32, NULL, NULL, 0);
+}
+
+static inline void bit_spin_lock(int nr, unsigned long *_addr)
+{
+	unsigned long mask;
+	unsigned long *addr = _addr + (nr / BITS_PER_LONG);
+	unsigned long v;
+
+	nr &= BITS_PER_LONG - 1;
+	mask = 1UL << nr;
+
+	while (1) {
+		v = __atomic_fetch_or(addr, mask, __ATOMIC_ACQUIRE);
+		if (!(v & mask))
+			break;
+
+		do_futex(nr, addr, v, FUTEX_WAIT);
+	}
+}
+
+static inline void bit_spin_wake(int nr, unsigned long *_addr)
+{
+	do_futex(nr, _addr, INT_MAX, FUTEX_WAKE);
+}
+
+static inline void bit_spin_unlock(int nr, unsigned long *_addr)
+{
+	unsigned long mask;
+	unsigned long *addr = _addr + (nr / BITS_PER_LONG);
+
+	nr &= BITS_PER_LONG - 1;
+	mask = 1UL << nr;
+
+	__atomic_and_fetch(addr, ~mask, __ATOMIC_RELEASE);
+	do_futex(nr, addr, INT_MAX, FUTEX_WAKE);
+}
+
+#endif /* __LINUX_BIT_SPINLOCK_H */
+