Re: [RFC PATCH 01/13] futex2: Implement wait and wake functions

+/* kernel/futex2.c */
+asmlinkage long sys_futex_wait(void __user *uaddr, unsigned int val,
+			       unsigned int flags,
+			       struct __kernel_timespec __user __user *timo);

+asmlinkage long sys_futex_wake(void __user *uaddr, unsigned int nr_wake,
+			       unsigned int flags);
+
 /* kernel/hrtimer.c */
 asmlinkage long sys_nanosleep(struct __kernel_timespec __user *rqtp,
 			      struct __kernel_timespec __user *rmtp);

diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 728752917785..57e19200f7e4 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h

@@ -862,8 +862,14 @@ __SYSCALL(__NR_process_madvise, sys_process_madvise)
 #define __NR_epoll_pwait2 441
 __SC_COMP(__NR_epoll_pwait2, sys_epoll_pwait2, compat_sys_epoll_pwait2)
 
+#define __NR_futex_wait 442
+__SYSCALL(__NR_futex_wait, sys_futex_wait)
+
+#define __NR_futex_wake 443
+__SYSCALL(__NR_futex_wake, sys_futex_wake)
+
 #undef __NR_syscalls
-#define __NR_syscalls 442
+#define __NR_syscalls 444
 
 /*
  * 32 bit systems traditionally used different

diff --git a/include/uapi/linux/futex.h b/include/uapi/linux/futex.h
index a89eb0accd5e..9fbdaaf4f254 100644
--- a/include/uapi/linux/futex.h
+++ b/include/uapi/linux/futex.h

@@ -41,6 +41,62 @@
 #define FUTEX_CMP_REQUEUE_PI_PRIVATE	(FUTEX_CMP_REQUEUE_PI | \
 					 FUTEX_PRIVATE_FLAG)
 
+/* Size argument to futex2 syscall */
+#define FUTEX_8		0
+#define FUTEX_16	1
+#define FUTEX_32	2
+
+#define FUTEX_SIZE_MASK	0x3
+
+#define FUTEX_SHARED_FLAG 8
+
+#define FUTEX_NUMA_FLAG 16
+
+/**
+ * struct futexXX_numa - struct for NUMA-aware futex operation
+ * @value: futex value
+ * @hint:  node id to operate
+ */
+
+struct futex8_numa {
+	__u8 value;
+	__s8 hint;
+};
+
+struct futex16_numa {
+	__u16 value;
+	__s16 hint;
+};
+
+struct futex32_numa {
+	__u32 value;
+	__s32 hint;
+};

+
+#define FUTEX_WAITV_MAX 128
+
+/**
+ * struct futex_waitv - A waiter for vectorized wait
+ * @uaddr: User address to wait on
+ * @val:   Expected value at uaddr
+ * @flags: Flags for this waiter
+ */
+struct futex_waitv {
+	void *uaddr;
+	unsigned int val;
+	unsigned int flags;
+};

+
+/**
+ * struct futex_requeue - Define an address and its flags for requeue operation
+ * @uaddr: User address of one of the requeue arguments
+ * @flags: Flags for this address
+ */
+struct futex_requeue {
+	void *uaddr;
+	unsigned int flags;
+};

+/**
+ * struct futexv_head - List of futexes to be waited
+ * @task:    Task to be awaken
+ * @hint:    Was someone on this list awakened?
+ * @objects: List of futexes
+ */
+struct futexv_head {
+	struct task_struct *task;
+	bool hint;
+	struct futex_waiter objects[0];
+};

+
+/**
+ * struct futex_bucket - A bucket of futex's hash table
+ * @waiters: Number of waiters in the bucket
+ * @lock:    Bucket lock
+ * @list:    List of waiters on this bucket
+ */
+struct futex_bucket {
+	atomic_t waiters;
+	spinlock_t lock;
+	struct list_head list;
+};
+
+/**
+ * struct futex_single_waiter - Wrapper for a futexv_head of one element
+ * @futexv: Single futexv element
+ * @waiter: Single waiter element
+ */
+struct futex_single_waiter {
+	struct futexv_head futexv;
+	struct futex_waiter waiter;
+} __packed;

+
+/* Mask for futex2 flag operations */
+#define FUTEX2_MASK (FUTEX_SIZE_MASK | FUTEX_SHARED_FLAG | \
+		     FUTEX_CLOCK_REALTIME)

+
+/* Mask for sys_futex_waitv flag */
+#define FUTEXV_MASK (FUTEX_CLOCK_REALTIME)
+
+/* Mask for each futex in futex_waitv list */
+#define FUTEXV_WAITER_MASK (FUTEX_SIZE_MASK | FUTEX_SHARED_FLAG)
+
+struct futex_bucket *futex_table;
+unsigned int futex2_hashsize;
+
+/*
+ * Reflects a new waiter being added to the waitqueue.
+ */
+static inline void bucket_inc_waiters(struct futex_bucket *bucket)
+{
+#ifdef CONFIG_SMP
+	atomic_inc(&bucket->waiters);
+	/*
+	 * Issue a barrier after adding so futex_wake() will see that the
+	 * value had increased
+	 */
+	smp_mb__after_atomic();
+#endif
+}
+
+/*
+ * Reflects a waiter being removed from the waitqueue by wakeup
+ * paths.
+ */
+static inline void bucket_dec_waiters(struct futex_bucket *bucket)
+{
+#ifdef CONFIG_SMP
+	atomic_dec(&bucket->waiters);
+#endif
+}
+
+/*
+ * Get the number of waiters in a bucket
+ */
+static inline int bucket_get_waiters(struct futex_bucket *bucket)
+{
+#ifdef CONFIG_SMP
+	/*
+	 * Issue a barrier before reading so we get an updated value from
+	 * futex_wait()
+	 */
+	smp_mb();
+	return atomic_read(&bucket->waiters);
+#else
+	return 1;
+#endif
+}
+
+/**
+ * futex_get_bucket - Check if the user address is valid, prepare internal
+ *                    data and calculate the hash
+ * @uaddr:   futex user address
+ * @key:     data that uniquely identifies a futex
+ *
+ * Return: address of bucket on success, error code otherwise
+ */
+static struct futex_bucket *futex_get_bucket(void __user *uaddr,
+					     struct futex_key *key)
+{
+	uintptr_t address = (uintptr_t)uaddr;
+	u32 hash_key;
+
+	/* Checking if uaddr is valid and accessible */
+	if (unlikely(!IS_ALIGNED(address, sizeof(u32))))
+		return ERR_PTR(-EINVAL);
+	if (unlikely(!access_ok(address, sizeof(u32))))
+		return ERR_PTR(-EFAULT);

+
+	key->offset = address % PAGE_SIZE;
+	address -= key->offset;
+	key->pointer = (u64)address;
+	key->index = (unsigned long)current->mm;

+
+	/* Generate hash key for this futex using uaddr and current->mm */
+	hash_key = jhash2((u32 *)key, sizeof(*key) / sizeof(u32), 0);
+
+	/* Since HASH_SIZE is 2^n, subtracting 1 makes a perfect bit mask */
+	return &futex_table[hash_key & (futex2_hashsize - 1)];

+static int futex_enqueue(struct futexv_head *futexv, unsigned int nr_futexes,
+			 int *awakened)
+{
+	int i, ret;
+	u32 uval, *uaddr, val;
+	struct futex_bucket *bucket;
+
+retry:
+	set_current_state(TASK_INTERRUPTIBLE);
+
+	for (i = 0; i < nr_futexes; i++) {
+		uaddr = (u32 * __user)futexv->objects[i].uaddr;
+		val = (u32)futexv->objects[i].val;
+
+		bucket = futexv->objects[i].bucket;
+
+		bucket_inc_waiters(bucket);
+		spin_lock(&bucket->lock);
+
+		ret = futex_get_user(&uval, uaddr);
+
+		if (unlikely(ret)) {
+			spin_unlock(&bucket->lock);
+
+			bucket_dec_waiters(bucket);
+			__set_current_state(TASK_RUNNING);
+			*awakened = futex_dequeue_multiple(futexv, i);
+
+			if (__get_user(uval, uaddr))
+				return -EFAULT;
+
+			if (*awakened >= 0)
+				return 1;

+/**
+ * futex_wait - Setup the timer (if there's one) and wait on a list of futexes
+ * @futexv:     List of futexes
+ * @nr_futexes: Length of futexv
+ * @timo:	Timeout
+ * @flags:	Timeout flags
+ *
+ * Return:
+ * * 0 >= - Hint of which futex woke us
+ * * 0 <  - Error code
+ */
+static int futex_set_timer_and_wait(struct futexv_head *futexv,
+				    unsigned int nr_futexes,
+				    struct __kernel_timespec __user *timo,
+				    unsigned int flags)
+{
+	struct hrtimer_sleeper timeout;
+	int ret;
+
+	if (timo) {
+		ret = futex_setup_time(timo, &timeout, flags);
+		if (ret)
+			return ret;
+	}
+
+	ret = __futex_wait(futexv, nr_futexes, timo ? &timeout : NULL);
+
+	if (timo)
+		hrtimer_cancel(&timeout.timer);
+
+	return ret;
+}