v4.19.13 snapshot.
diff --git a/include/linux/futex.h b/include/linux/futex.h
new file mode 100644
index 0000000..821ae50
--- /dev/null
+++ b/include/linux/futex.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_FUTEX_H
+#define _LINUX_FUTEX_H
+
+#include <linux/ktime.h>
+#include <uapi/linux/futex.h>
+
+struct inode;
+struct mm_struct;
+struct task_struct;
+
+extern int
+handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi);
+
+/*
+ * Futexes are matched on equal values of this key.
+ * The key type depends on whether it's a shared or private mapping.
+ * Don't rearrange members without looking at hash_futex().
+ *
+ * offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
+ * We use the two low order bits of offset to tell what is the kind of key :
+ * 00 : Private process futex (PTHREAD_PROCESS_PRIVATE)
+ * (no reference on an inode or mm)
+ * 01 : Shared futex (PTHREAD_PROCESS_SHARED)
+ * mapped on a file (reference on the underlying inode)
+ * 10 : Shared futex (PTHREAD_PROCESS_SHARED)
+ * (but private mapping on an mm, and reference taken on it)
+*/
+
+#define FUT_OFF_INODE 1 /* We set bit 0 if key has a reference on inode */
+#define FUT_OFF_MMSHARED 2 /* We set bit 1 if key has a reference on mm */
+
+union futex_key {
+ struct {
+ unsigned long pgoff;
+ struct inode *inode;
+ int offset;
+ } shared;
+ struct {
+ unsigned long address;
+ struct mm_struct *mm;
+ int offset;
+ } private;
+ struct {
+ unsigned long word;
+ void *ptr;
+ int offset;
+ } both;
+};
+
+#define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = NULL } }
+
+#ifdef CONFIG_FUTEX
+extern void exit_robust_list(struct task_struct *curr);
+
+long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
+ u32 __user *uaddr2, u32 val2, u32 val3);
+#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
+#define futex_cmpxchg_enabled 1
+#else
+extern int futex_cmpxchg_enabled;
+#endif
+#else
+static inline void exit_robust_list(struct task_struct *curr)
+{
+}
+
+static inline long do_futex(u32 __user *uaddr, int op, u32 val,
+ ktime_t *timeout, u32 __user *uaddr2,
+ u32 val2, u32 val3)
+{
+ return -EINVAL;
+}
+#endif
+
+#ifdef CONFIG_FUTEX_PI
+extern void exit_pi_state_list(struct task_struct *curr);
+#else
+static inline void exit_pi_state_list(struct task_struct *curr)
+{
+}
+#endif
+
+#endif