[PATCH v1 06/14] futex: Add sys_futex_wait()

From: Peter Zijlstra
Date: Fri Jul 21 2023 - 07:00:23 EST

To complement sys_futex_waitv()/wake(), add sys_futex_wait(). This
syscall implements what was previously known as FUTEX_WAIT_BITSET
except it uses 'unsigned long' for the value and bitmask arguments,
takes timespec and clockid_t arguments for the absolute timeout and
uses FUTEX2 flags.

The 'unsigned long' allows FUTEX2_64 on 64bit platforms.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/alpha/kernel/syscalls/syscall.tbl | 1
arch/arm/tools/syscall.tbl | 1
arch/arm64/include/asm/unistd32.h | 2
arch/ia64/kernel/syscalls/syscall.tbl | 1
arch/m68k/kernel/syscalls/syscall.tbl | 1
arch/microblaze/kernel/syscalls/syscall.tbl | 1
arch/mips/kernel/syscalls/syscall_n32.tbl | 1
arch/mips/kernel/syscalls/syscall_n64.tbl | 1
arch/mips/kernel/syscalls/syscall_o32.tbl | 1
arch/parisc/kernel/syscalls/syscall.tbl | 1
arch/powerpc/kernel/syscalls/syscall.tbl | 1
arch/s390/kernel/syscalls/syscall.tbl | 1
arch/sh/kernel/syscalls/syscall.tbl | 1
arch/sparc/kernel/syscalls/syscall.tbl | 1
arch/x86/entry/syscalls/syscall_32.tbl | 1
arch/x86/entry/syscalls/syscall_64.tbl | 1
arch/xtensa/kernel/syscalls/syscall.tbl | 1
include/linux/syscalls.h | 4
include/uapi/asm-generic/unistd.h | 4
kernel/futex/futex.h | 3
kernel/futex/syscalls.c | 120 +++++++++++++++++++++-------
kernel/futex/waitwake.c | 65 ++++++++-------
kernel/sys_ni.c | 1
23 files changed, 156 insertions(+), 59 deletions(-)

--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -492,3 +492,4 @@
560 common set_mempolicy_home_node sys_ni_syscall
561 common cachestat sys_cachestat
562 common futex_wake sys_futex_wake
+563 common futex_wait sys_futex_wait
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -466,3 +466,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -911,6 +911,8 @@ __SYSCALL(__NR_set_mempolicy_home_node,
__SYSCALL(__NR_cachestat, sys_cachestat)
#define __NR_futex_wake 452
__SYSCALL(__NR_futex_wake, sys_futex_wake)
+#define __NR_futex_wait 453
+__SYSCALL(__NR_futex_wait, sys_futex_wait)

/*
* Please add new compat syscalls above this comment and update
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -373,3 +373,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -452,3 +452,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -458,3 +458,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -391,3 +391,4 @@
450 n32 set_mempolicy_home_node sys_set_mempolicy_home_node
451 n32 cachestat sys_cachestat
452 n32 futex_wake sys_futex_wake
+453 n32 futex_wait sys_futex_wait
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -367,3 +367,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 n64 cachestat sys_cachestat
452 n64 futex_wake sys_futex_wake
+453 n64 futex_wait sys_futex_wait
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -440,3 +440,4 @@
450 o32 set_mempolicy_home_node sys_set_mempolicy_home_node
451 o32 cachestat sys_cachestat
452 o32 futex_wake sys_futex_wake
+453 o32 futex_wait sys_futex_wait
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -451,3 +451,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -539,3 +539,4 @@
450 nospu set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -455,3 +455,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat sys_cachestat
452 common futex_wake sys_futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait sys_futex_wait
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -455,3 +455,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -498,3 +498,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -457,3 +457,4 @@
450 i386 set_mempolicy_home_node sys_set_mempolicy_home_node
451 i386 cachestat sys_cachestat
452 i386 futex_wake sys_futex_wake
+453 i386 futex_wait sys_futex_wait
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -374,6 +374,7 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait

#
# Due to a historical design error, certain syscalls are numbered differently
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -423,3 +423,4 @@
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common futex_wake sys_futex_wake
+453 common futex_wait sys_futex_wait
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -566,6 +566,10 @@ asmlinkage long sys_futex_waitv(struct f

asmlinkage long sys_futex_wake(void __user *uaddr, unsigned long mask, int nr, unsigned int flags);

+asmlinkage long sys_futex_wait(void __user *uaddr, unsigned long val, unsigned long mask,
+ unsigned int flags, struct __kernel_timespec __user *timespec,
+ clockid_t clockid);
+
asmlinkage long sys_nanosleep(struct __kernel_timespec __user *rqtp,
struct __kernel_timespec __user *rmtp);
asmlinkage long sys_nanosleep_time32(struct old_timespec32 __user *rqtp,
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -820,9 +820,11 @@ __SYSCALL(__NR_set_mempolicy_home_node,
__SYSCALL(__NR_cachestat, sys_cachestat)
#define __NR_futex_wake 452
__SYSCALL(__NR_futex_wake, sys_futex_wake)
+#define __NR_futex_wait 453
+__SYSCALL(__NR_futex_wait, sys_futex_wait)

#undef __NR_syscalls
-#define __NR_syscalls 453
+#define __NR_syscalls 454

/*
* 32 bit systems traditionally used different
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -330,6 +330,9 @@ extern int futex_requeue(u32 __user *uad
u32 __user *uaddr2, int nr_wake, int nr_requeue,
u32 *cmpval, int requeue_pi);

+extern int __futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
+ struct hrtimer_sleeper *to, u32 bitset);
+
extern int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
ktime_t *abs_time, u32 bitset);

--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -221,6 +221,46 @@ static int futex_parse_waitv(struct fute
return 0;
}

+static int futex2_setup_timeout(struct __kernel_timespec __user *timeout,
+ clockid_t clockid, struct hrtimer_sleeper *to)
+{
+ int flag_clkid = 0, flag_init = 0;
+ struct timespec64 ts;
+ ktime_t time;
+ int ret;
+
+ if (!timeout)
+ return 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);
+ return 0;
+}
+
+static inline void futex2_destroy_timeout(struct hrtimer_sleeper *to)
+{
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+}
+
/**
* sys_futex_waitv - Wait on a list of futexes
* @waiters: List of futexes to wait on
@@ -250,8 +290,6 @@ SYSCALL_DEFINE5(futex_waitv, struct fute
{
struct hrtimer_sleeper to;
struct futex_vector *futexv;
- struct timespec64 ts;
- ktime_t time;
int ret;

/* This syscall supports no flags for now */
@@ -261,30 +299,8 @@ SYSCALL_DEFINE5(futex_waitv, struct fute
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);
- }
+ if (timeout && (ret = futex2_setup_timeout(timeout, clockid, &to)))
+ return ret;

futexv = kcalloc(nr_futexes, sizeof(*futexv), GFP_KERNEL);
if (!futexv) {
@@ -299,10 +315,8 @@ SYSCALL_DEFINE5(futex_waitv, struct fute
kfree(futexv);

destroy_timer:
- if (timeout) {
- hrtimer_cancel(&to.timer);
- destroy_hrtimer_on_stack(&to.timer);
- }
+ if (timeout)
+ futex2_destroy_timeout(&to);
return ret;
}

@@ -336,6 +350,52 @@ SYSCALL_DEFINE4(futex_wake,
return futex_wake(uaddr, flags, nr, mask);
}

+/*
+ * sys_futex_wait - Wait on a futex
+ * @uaddr: Address of the futex to wait on
+ * @val: Value of @uaddr
+ * @mask: bitmask
+ * @flags: FUTEX2 flags
+ * @timeout: Optional absolute timeout
+ * @clockid: Clock to be used for the timeout, realtime or monotonic
+ *
+ * Identical to the traditional FUTEX_WAIT_BITSET op, except it is part of the
+ * futex2 familiy of calls.
+ */
+
+SYSCALL_DEFINE6(futex_wait,
+ void __user *, uaddr,
+ unsigned long, val,
+ unsigned long, mask,
+ unsigned int, flags,
+ struct __kernel_timespec __user *, timeout,
+ clockid_t, clockid)
+{
+ struct hrtimer_sleeper to;
+ int ret;
+
+ if (flags & ~FUTEX2_MASK)
+ return -EINVAL;
+
+ flags = futex2_to_flags(flags);
+ if (!futex_flags_valid(flags))
+ return -EINVAL;
+
+ if (!futex_validate_input(flags, val) ||
+ !futex_validate_input(flags, mask))
+ return -EINVAL;
+
+ if (timeout && (ret = futex2_setup_timeout(timeout, clockid, &to)))
+ return ret;
+
+ ret = __futex_wait(uaddr, flags, val, timeout ? &to : NULL, mask);
+
+ if (timeout)
+ futex2_destroy_timeout(&to);
+
+ return ret;
+}
+
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE2(set_robust_list,
struct compat_robust_list_head __user *, head,
--- a/kernel/futex/waitwake.c
+++ b/kernel/futex/waitwake.c
@@ -629,20 +629,18 @@ int futex_wait_setup(u32 __user *uaddr,
return ret;
}

-int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, ktime_t *abs_time, u32 bitset)
+int __futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
+ struct hrtimer_sleeper *to, u32 bitset)
{
- struct hrtimer_sleeper timeout, *to;
- struct restart_block *restart;
- struct futex_hash_bucket *hb;
struct futex_q q = futex_q_init;
+ struct futex_hash_bucket *hb;
int ret;

if (!bitset)
return -EINVAL;
+
q.bitset = bitset;

- to = futex_setup_timer(abs_time, &timeout, flags,
- current->timer_slack_ns);
retry:
/*
* Prepare to wait on uaddr. On success, it holds hb->lock and q
@@ -650,18 +648,17 @@ int futex_wait(u32 __user *uaddr, unsign
*/
ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
if (ret)
- goto out;
+ return ret;

/* futex_queue and wait for wakeup, timeout, or a signal. */
futex_wait_queue(hb, &q, to);

/* If we were woken (and unqueued), we succeeded, whatever. */
- ret = 0;
if (!futex_unqueue(&q))
- goto out;
- ret = -ETIMEDOUT;
+ return 0;
+
if (to && !to->task)
- goto out;
+ return -ETIMEDOUT;

/*
* We expect signal_pending(current), but we might be the
@@ -670,24 +667,36 @@ int futex_wait(u32 __user *uaddr, unsign
if (!signal_pending(current))
goto retry;

- ret = -ERESTARTSYS;
- if (!abs_time)
- goto out;
-
- restart = &current->restart_block;
- restart->futex.uaddr = uaddr;
- restart->futex.val = val;
- restart->futex.time = *abs_time;
- restart->futex.bitset = bitset;
- restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
-
- ret = set_restart_fn(restart, futex_wait_restart);
-
-out:
- if (to) {
- hrtimer_cancel(&to->timer);
- destroy_hrtimer_on_stack(&to->timer);
+ return -ERESTARTSYS;
+}
+
+int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, ktime_t *abs_time, u32 bitset)
+{
+ struct hrtimer_sleeper timeout, *to;
+ struct restart_block *restart;
+ int ret;
+
+ to = futex_setup_timer(abs_time, &timeout, flags,
+ current->timer_slack_ns);
+
+ ret = __futex_wait(uaddr, flags, val, to, bitset);
+ if (!to)
+ return ret;
+
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+
+ if (ret == -ERESTARTSYS) {
+ restart = &current->restart_block;
+ restart->futex.uaddr = uaddr;
+ restart->futex.val = val;
+ restart->futex.time = *abs_time;
+ restart->futex.bitset = bitset;
+ restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
+
+ return set_restart_fn(restart, futex_wait_restart);
}
+
return ret;
}

--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -88,6 +88,7 @@ COND_SYSCALL(get_robust_list);
COND_SYSCALL_COMPAT(get_robust_list);
COND_SYSCALL(futex_waitv);
COND_SYSCALL(futex_wake);
+COND_SYSCALL(futex_wait);
COND_SYSCALL(kexec_load);
COND_SYSCALL_COMPAT(kexec_load);
COND_SYSCALL(init_module);