kernel/futex/syscalls.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later

 #include <linux/compat.h>
 #include <linux/syscalls.h>
 #include <linux/time_namespace.h>

 #include "futex.h"

 /*
  * Support for robust futexes: the kernel cleans up held futexes at
  * thread exit time.
  *
  * Implementation: user-space maintains a per-thread list of locks it
  * is holding. Upon do_exit(), the kernel carefully walks this list,
  * and marks all locks that are owned by this thread with the
  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
  * always manipulated with the lock held, so the list is private and
  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
  * field, to allow the kernel to clean up if the thread dies after
  * acquiring the lock, but just before it could have added itself to
  * the list. There can only be one such pending lock.
  */

 /**
  * sys_set_robust_list() - Set the robust-futex list head of a task
  * @head:	pointer to the list-head
  * @len:	length of the list-head, as userspace expects
  */
 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
 		size_t, len)
 {
 	/*
 	 * The kernel knows only one size for now:
 	 */
 	if (unlikely(len != sizeof(*head)))
 		return -EINVAL;

 	current->robust_list = head;

 	return 0;
 }

 /**
  * sys_get_robust_list() - Get the robust-futex list head of a task
  * @pid:	pid of the process [zero for current task]
  * @head_ptr:	pointer to a list-head pointer, the kernel fills it in
  * @len_ptr:	pointer to a length field, the kernel fills in the header size
  */
 SYSCALL_DEFINE3(get_robust_list, int, pid,
 		struct robust_list_head __user * __user *, head_ptr,
 		size_t __user *, len_ptr)
 {
 	struct robust_list_head __user *head;
 	unsigned long ret;
 	struct task_struct *p;

 	rcu_read_lock();

 	ret = -ESRCH;
 	if (!pid)
 		p = current;
 	else {
 		p = find_task_by_vpid(pid);
 		if (!p)
 			goto err_unlock;
 	}

 	ret = -EPERM;
 	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
 		goto err_unlock;

 	head = p->robust_list;
 	rcu_read_unlock();

 	if (put_user(sizeof(*head), len_ptr))
 		return -EFAULT;
 	return put_user(head, head_ptr);

 err_unlock:
 	rcu_read_unlock();

 	return ret;
 }

 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 		u32 __user *uaddr2, u32 val2, u32 val3)
 {
 	int cmd = op & FUTEX_CMD_MASK;
 	unsigned int flags = 0;

 	if (!(op & FUTEX_PRIVATE_FLAG))
 		flags |= FLAGS_SHARED;

 	if (op & FUTEX_CLOCK_REALTIME) {
 		flags |= FLAGS_CLOCKRT;
 		if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
 		    cmd != FUTEX_LOCK_PI2)
 			return -ENOSYS;
 	}

 	switch (cmd) {
 	case FUTEX_WAIT:
 		val3 = FUTEX_BITSET_MATCH_ANY;
 		fallthrough;
 	case FUTEX_WAIT_BITSET:
 		return futex_wait(uaddr, flags, val, timeout, val3);
 	case FUTEX_WAKE:
 		val3 = FUTEX_BITSET_MATCH_ANY;
 		fallthrough;
 	case FUTEX_WAKE_BITSET:
 		return futex_wake(uaddr, flags, val, val3);
 	case FUTEX_REQUEUE:
 		return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
 	case FUTEX_CMP_REQUEUE:
 		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
 	case FUTEX_WAKE_OP:
 		return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
 	case FUTEX_LOCK_PI:
 		flags |= FLAGS_CLOCKRT;
 		fallthrough;
 	case FUTEX_LOCK_PI2:
 		return futex_lock_pi(uaddr, flags, timeout, 0);
 	case FUTEX_UNLOCK_PI:
 		return futex_unlock_pi(uaddr, flags);
 	case FUTEX_TRYLOCK_PI:
 		return futex_lock_pi(uaddr, flags, NULL, 1);
 	case FUTEX_WAIT_REQUEUE_PI:
 		val3 = FUTEX_BITSET_MATCH_ANY;
 		return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
 					     uaddr2);
 	case FUTEX_CMP_REQUEUE_PI:
 		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
 	}
 	return -ENOSYS;
 }

 static __always_inline bool futex_cmd_has_timeout(u32 cmd)
 {
 	switch (cmd) {
 	case FUTEX_WAIT:
 	case FUTEX_LOCK_PI:
 	case FUTEX_LOCK_PI2:
 	case FUTEX_WAIT_BITSET:
 	case FUTEX_WAIT_REQUEUE_PI:
 		return true;
 	}
 	return false;
 }

 static __always_inline int
 futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
 {
 	if (!timespec64_valid(ts))
 		return -EINVAL;

 	*t = timespec64_to_ktime(*ts);
 	if (cmd == FUTEX_WAIT)
 		*t = ktime_add_safe(ktime_get(), *t);
 	else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
 		*t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
 	return 0;
 }

 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
 		const struct __kernel_timespec __user *, utime,
 		u32 __user *, uaddr2, u32, val3)
 {
 	int ret, cmd = op & FUTEX_CMD_MASK;
 	ktime_t t, *tp = NULL;
 	struct timespec64 ts;

 	if (utime && futex_cmd_has_timeout(cmd)) {
 		if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
 			return -EFAULT;
 		if (get_timespec64(&ts, utime))
 			return -EFAULT;
 		ret = futex_init_timeout(cmd, op, &ts, &t);
 		if (ret)
 			return ret;
 		tp = &t;
 	}

 	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
 }

 /* Mask of available flags for each futex in futex_waitv list */
 #define FUTEXV_WAITER_MASK (FUTEX_32 | FUTEX_PRIVATE_FLAG)

 /**
  * futex_parse_waitv - Parse a waitv array from userspace
  * @futexv:	Kernel side list of waiters to be filled
  * @uwaitv:     Userspace list to be parsed
  * @nr_futexes: Length of futexv
  *
  * Return: Error code on failure, 0 on success
  */
 static int futex_parse_waitv(struct futex_vector *futexv,
 			     struct futex_waitv __user *uwaitv,
 			     unsigned int nr_futexes)
 {
 	struct futex_waitv aux;
 	unsigned int i;

 	for (i = 0; i < nr_futexes; i++) {
 		if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
 			return -EFAULT;

 		if ((aux.flags & ~FUTEXV_WAITER_MASK) || aux.__reserved)
 			return -EINVAL;

 		if (!(aux.flags & FUTEX_32))
 			return -EINVAL;

 		futexv[i].w.flags = aux.flags;
 		futexv[i].w.val = aux.val;
 		futexv[i].w.uaddr = aux.uaddr;
 		futexv[i].q = futex_q_init;
 	}

 	return 0;
 }

 /**
  * sys_futex_waitv - Wait on a list of futexes
  * @waiters:    List of futexes to wait on
  * @nr_futexes: Length of futexv
  * @flags:      Flag for timeout (monotonic/realtime)
  * @timeout:	Optional absolute timeout.
  * @clockid:	Clock to be used for the timeout, realtime or monotonic.
  *
  * Given an array of `struct futex_waitv`, wait on each uaddr. The thread wakes
  * if a futex_wake() is performed at any uaddr. The syscall returns immediately
  * if any waiter has *uaddr != val. *timeout is an optional timeout value for
  * the operation. Each waiter has individual flags. The `flags` argument for
  * the syscall should be used solely for specifying the timeout as realtime, if
  * needed. Flags for private futexes, sizes, etc. should be used on the
  * individual flags of each waiter.
  *
  * Returns the array index of one of the woken futexes. No further information
  * is provided: any number of other futexes may also have been woken by the
  * same event, and if more than one futex was woken, the retrned index may
  * refer to any one of them. (It is not necessaryily the futex with the
  * smallest index, nor the one most recently woken, nor...)
  */

 SYSCALL_DEFINE5(futex_waitv, struct futex_waitv __user *, waiters,
 		unsigned int, nr_futexes, unsigned int, flags,
 		struct __kernel_timespec __user *, timeout, clockid_t, clockid)
 {
 	struct hrtimer_sleeper to;
 	struct futex_vector *futexv;
 	struct timespec64 ts;
 	ktime_t time;
 	int ret;

 	/* This syscall supports no flags for now */
 	if (flags)
 		return -EINVAL;

 	if (!nr_futexes || nr_futexes > FUTEX_WAITV_MAX || !waiters)
 		return -EINVAL;

 	if (timeout) {
 		int flag_clkid = 0, flag_init = 0;

 		if (clockid == CLOCK_REALTIME) {
 			flag_clkid = FLAGS_CLOCKRT;
 			flag_init = FUTEX_CLOCK_REALTIME;
 		}

 		if (clockid != CLOCK_REALTIME && clockid != CLOCK_MONOTONIC)
 			return -EINVAL;

 		if (get_timespec64(&ts, timeout))
 			return -EFAULT;

 		/*
 		 * Since there's no opcode for futex_waitv, use
 		 * FUTEX_WAIT_BITSET that uses absolute timeout as well
 		 */
 		ret = futex_init_timeout(FUTEX_WAIT_BITSET, flag_init, &ts, &time);
 		if (ret)
 			return ret;

 		futex_setup_timer(&time, &to, flag_clkid, 0);
 	}

 	futexv = kcalloc(nr_futexes, sizeof(*futexv), GFP_KERNEL);
 	if (!futexv)
 		return -ENOMEM;

 	ret = futex_parse_waitv(futexv, waiters, nr_futexes);
 	if (!ret)
 		ret = futex_wait_multiple(futexv, nr_futexes, timeout ? &to : NULL);

 	if (timeout) {
 		hrtimer_cancel(&to.timer);
 		destroy_hrtimer_on_stack(&to.timer);
 	}

 	kfree(futexv);
 	return ret;
 }

 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE2(set_robust_list,
 		struct compat_robust_list_head __user *, head,
 		compat_size_t, len)
 {
 	if (unlikely(len != sizeof(*head)))
 		return -EINVAL;

 	current->compat_robust_list = head;

 	return 0;
 }

 COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
 			compat_uptr_t __user *, head_ptr,
 			compat_size_t __user *, len_ptr)
 {
 	struct compat_robust_list_head __user *head;
 	unsigned long ret;
 	struct task_struct *p;

 	rcu_read_lock();

 	ret = -ESRCH;
 	if (!pid)
 		p = current;
 	else {
 		p = find_task_by_vpid(pid);
 		if (!p)
 			goto err_unlock;
 	}

 	ret = -EPERM;
 	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
 		goto err_unlock;

 	head = p->compat_robust_list;
 	rcu_read_unlock();

 	if (put_user(sizeof(*head), len_ptr))
 		return -EFAULT;
 	return put_user(ptr_to_compat(head), head_ptr);

 err_unlock:
 	rcu_read_unlock();

 	return ret;
 }
 #endif /* CONFIG_COMPAT */

 #ifdef CONFIG_COMPAT_32BIT_TIME
 SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
 		const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
 		u32, val3)
 {
 	int ret, cmd = op & FUTEX_CMD_MASK;
 	ktime_t t, *tp = NULL;
 	struct timespec64 ts;

 	if (utime && futex_cmd_has_timeout(cmd)) {
 		if (get_old_timespec32(&ts, utime))
 			return -EFAULT;
 		ret = futex_init_timeout(cmd, op, &ts, &t);
 		if (ret)
 			return ret;
 		tp = &t;
 	}

 	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
 }
 #endif /* CONFIG_COMPAT_32BIT_TIME */
	// SPDX-License-Identifier: GPL-2.0-or-later

	#include <linux/compat.h>
	#include <linux/syscalls.h>
	#include <linux/time_namespace.h>

	#include "futex.h"

	/*
	* Support for robust futexes: the kernel cleans up held futexes at
	* thread exit time.
	*
	* Implementation: user-space maintains a per-thread list of locks it
	* is holding. Upon do_exit(), the kernel carefully walks this list,
	* and marks all locks that are owned by this thread with the
	* FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
	* always manipulated with the lock held, so the list is private and
	* per-thread. Userspace also maintains a per-thread 'list_op_pending'
	* field, to allow the kernel to clean up if the thread dies after
	* acquiring the lock, but just before it could have added itself to
	* the list. There can only be one such pending lock.
	*/

	/**
	* sys_set_robust_list() - Set the robust-futex list head of a task
	* @head: pointer to the list-head
	* @len: length of the list-head, as userspace expects
	*/
	SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
	size_t, len)
	{
	/*
	* The kernel knows only one size for now:
	*/
	if (unlikely(len != sizeof(*head)))
	return -EINVAL;

	current->robust_list = head;

	return 0;
	}

	/**
	* sys_get_robust_list() - Get the robust-futex list head of a task
	* @pid: pid of the process [zero for current task]
	* @head_ptr: pointer to a list-head pointer, the kernel fills it in
	* @len_ptr: pointer to a length field, the kernel fills in the header size
	*/
	SYSCALL_DEFINE3(get_robust_list, int, pid,
	struct robust_list_head __user * __user *, head_ptr,
	size_t __user *, len_ptr)
	{
	struct robust_list_head __user *head;
	unsigned long ret;
	struct task_struct *p;

	rcu_read_lock();

	ret = -ESRCH;
	if (!pid)
	p = current;
	else {
	p = find_task_by_vpid(pid);
	if (!p)
	goto err_unlock;
	}

	ret = -EPERM;
	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
	goto err_unlock;

	head = p->robust_list;
	rcu_read_unlock();

	if (put_user(sizeof(*head), len_ptr))
	return -EFAULT;
	return put_user(head, head_ptr);

	err_unlock:
	rcu_read_unlock();

	return ret;
	}

	long do_futex(u32 __user uaddr, int op, u32 val, ktime_t timeout,
	u32 __user *uaddr2, u32 val2, u32 val3)
	{
	int cmd = op & FUTEX_CMD_MASK;
	unsigned int flags = 0;

	if (!(op & FUTEX_PRIVATE_FLAG))
	flags \|= FLAGS_SHARED;

	if (op & FUTEX_CLOCK_REALTIME) {
	flags \|= FLAGS_CLOCKRT;
	if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
	cmd != FUTEX_LOCK_PI2)
	return -ENOSYS;
	}

	switch (cmd) {
	case FUTEX_WAIT:
	val3 = FUTEX_BITSET_MATCH_ANY;
	fallthrough;
	case FUTEX_WAIT_BITSET:
	return futex_wait(uaddr, flags, val, timeout, val3);
	case FUTEX_WAKE:
	val3 = FUTEX_BITSET_MATCH_ANY;
	fallthrough;
	case FUTEX_WAKE_BITSET:
	return futex_wake(uaddr, flags, val, val3);
	case FUTEX_REQUEUE:
	return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
	case FUTEX_CMP_REQUEUE:
	return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
	case FUTEX_WAKE_OP:
	return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
	case FUTEX_LOCK_PI:
	flags \|= FLAGS_CLOCKRT;
	fallthrough;
	case FUTEX_LOCK_PI2:
	return futex_lock_pi(uaddr, flags, timeout, 0);
	case FUTEX_UNLOCK_PI:
	return futex_unlock_pi(uaddr, flags);
	case FUTEX_TRYLOCK_PI:
	return futex_lock_pi(uaddr, flags, NULL, 1);
	case FUTEX_WAIT_REQUEUE_PI:
	val3 = FUTEX_BITSET_MATCH_ANY;
	return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
	uaddr2);
	case FUTEX_CMP_REQUEUE_PI:
	return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
	}
	return -ENOSYS;
	}

	static __always_inline bool futex_cmd_has_timeout(u32 cmd)
	{
	switch (cmd) {
	case FUTEX_WAIT:
	case FUTEX_LOCK_PI:
	case FUTEX_LOCK_PI2:
	case FUTEX_WAIT_BITSET:
	case FUTEX_WAIT_REQUEUE_PI:
	return true;
	}
	return false;
	}

	static __always_inline int
	futex_init_timeout(u32 cmd, u32 op, struct timespec64 ts, ktime_t t)
	{
	if (!timespec64_valid(ts))
	return -EINVAL;

	t = timespec64_to_ktime(ts);
	if (cmd == FUTEX_WAIT)
	t = ktime_add_safe(ktime_get(), t);
	else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
	t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
	return 0;
	}

	SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
	const struct __kernel_timespec __user *, utime,
	u32 __user *, uaddr2, u32, val3)
	{
	int ret, cmd = op & FUTEX_CMD_MASK;
	ktime_t t, *tp = NULL;
	struct timespec64 ts;

	if (utime && futex_cmd_has_timeout(cmd)) {
	if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
	return -EFAULT;
	if (get_timespec64(&ts, utime))
	return -EFAULT;
	ret = futex_init_timeout(cmd, op, &ts, &t);
	if (ret)
	return ret;
	tp = &t;
	}

	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
	}

	/* Mask of available flags for each futex in futex_waitv list */
	#define FUTEXV_WAITER_MASK (FUTEX_32 \| FUTEX_PRIVATE_FLAG)

	/**
	* futex_parse_waitv - Parse a waitv array from userspace
	* @futexv: Kernel side list of waiters to be filled
	* @uwaitv: Userspace list to be parsed
	* @nr_futexes: Length of futexv
	*
	* Return: Error code on failure, 0 on success
	*/
	static int futex_parse_waitv(struct futex_vector *futexv,
	struct futex_waitv __user *uwaitv,
	unsigned int nr_futexes)
	{
	struct futex_waitv aux;
	unsigned int i;

	for (i = 0; i < nr_futexes; i++) {
	if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
	return -EFAULT;

	if ((aux.flags & ~FUTEXV_WAITER_MASK) \|\| aux.__reserved)
	return -EINVAL;

	if (!(aux.flags & FUTEX_32))
	return -EINVAL;

	futexv[i].w.flags = aux.flags;
	futexv[i].w.val = aux.val;
	futexv[i].w.uaddr = aux.uaddr;
	futexv[i].q = futex_q_init;
	}

	return 0;
	}

	/**
	* sys_futex_waitv - Wait on a list of futexes
	* @waiters: List of futexes to wait on
	* @nr_futexes: Length of futexv
	* @flags: Flag for timeout (monotonic/realtime)
	* @timeout: Optional absolute timeout.
	* @clockid: Clock to be used for the timeout, realtime or monotonic.
	*
	* Given an array of `struct futex_waitv`, wait on each uaddr. The thread wakes
	* if a futex_wake() is performed at any uaddr. The syscall returns immediately
	* if any waiter has uaddr != val. timeout is an optional timeout value for
	* the operation. Each waiter has individual flags. The `flags` argument for
	* the syscall should be used solely for specifying the timeout as realtime, if
	* needed. Flags for private futexes, sizes, etc. should be used on the
	* individual flags of each waiter.
	*
	* Returns the array index of one of the woken futexes. No further information
	* is provided: any number of other futexes may also have been woken by the
	* same event, and if more than one futex was woken, the retrned index may
	* refer to any one of them. (It is not necessaryily the futex with the
	* smallest index, nor the one most recently woken, nor...)
	*/

	SYSCALL_DEFINE5(futex_waitv, struct futex_waitv __user *, waiters,
	unsigned int, nr_futexes, unsigned int, flags,
	struct __kernel_timespec __user *, timeout, clockid_t, clockid)
	{
	struct hrtimer_sleeper to;
	struct futex_vector *futexv;
	struct timespec64 ts;
	ktime_t time;
	int ret;

	/* This syscall supports no flags for now */
	if (flags)
	return -EINVAL;

	if (!nr_futexes \|\| nr_futexes > FUTEX_WAITV_MAX \|\| !waiters)
	return -EINVAL;

	if (timeout) {
	int flag_clkid = 0, flag_init = 0;

	if (clockid == CLOCK_REALTIME) {
	flag_clkid = FLAGS_CLOCKRT;
	flag_init = FUTEX_CLOCK_REALTIME;
	}

	if (clockid != CLOCK_REALTIME && clockid != CLOCK_MONOTONIC)
	return -EINVAL;

	if (get_timespec64(&ts, timeout))
	return -EFAULT;

	/*
	* Since there's no opcode for futex_waitv, use
	* FUTEX_WAIT_BITSET that uses absolute timeout as well
	*/
	ret = futex_init_timeout(FUTEX_WAIT_BITSET, flag_init, &ts, &time);
	if (ret)
	return ret;

	futex_setup_timer(&time, &to, flag_clkid, 0);
	}

	futexv = kcalloc(nr_futexes, sizeof(*futexv), GFP_KERNEL);
	if (!futexv)
	return -ENOMEM;

	ret = futex_parse_waitv(futexv, waiters, nr_futexes);
	if (!ret)
	ret = futex_wait_multiple(futexv, nr_futexes, timeout ? &to : NULL);

	if (timeout) {
	hrtimer_cancel(&to.timer);
	destroy_hrtimer_on_stack(&to.timer);
	}

	kfree(futexv);
	return ret;
	}

	#ifdef CONFIG_COMPAT
	COMPAT_SYSCALL_DEFINE2(set_robust_list,
	struct compat_robust_list_head __user *, head,
	compat_size_t, len)
	{
	if (unlikely(len != sizeof(*head)))
	return -EINVAL;

	current->compat_robust_list = head;

	return 0;
	}

	COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
	compat_uptr_t __user *, head_ptr,
	compat_size_t __user *, len_ptr)
	{
	struct compat_robust_list_head __user *head;
	unsigned long ret;
	struct task_struct *p;

	rcu_read_lock();

	ret = -ESRCH;
	if (!pid)
	p = current;
	else {
	p = find_task_by_vpid(pid);
	if (!p)
	goto err_unlock;
	}

	ret = -EPERM;
	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
	goto err_unlock;

	head = p->compat_robust_list;
	rcu_read_unlock();

	if (put_user(sizeof(*head), len_ptr))
	return -EFAULT;
	return put_user(ptr_to_compat(head), head_ptr);

	err_unlock:
	rcu_read_unlock();

	return ret;
	}
	#endif /* CONFIG_COMPAT */

	#ifdef CONFIG_COMPAT_32BIT_TIME
	SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
	const struct old_timespec32 __user , utime, u32 __user , uaddr2,
	u32, val3)
	{
	int ret, cmd = op & FUTEX_CMD_MASK;
	ktime_t t, *tp = NULL;
	struct timespec64 ts;

	if (utime && futex_cmd_has_timeout(cmd)) {
	if (get_old_timespec32(&ts, utime))
	return -EFAULT;
	ret = futex_init_timeout(cmd, op, &ts, &t);
	if (ret)
	return ret;
	tp = &t;
	}

	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
	}
	#endif /* CONFIG_COMPAT_32BIT_TIME */