[RFC v2 0/4] futex2: Add new futex interface

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[RFC v2 0/4] futex2: Add new futex interface

Sourceware - libc-alpha mailing list
Hello,

This RFC is a followup to the previous discussion initiated from my last
patch "futex: Implement mechanism to wait on any of several futexes"[1].
As stated in the thread, the correct approach to move forward with the
wait multiple operation would be to create a new syscall that would have
all new cool features.

The first patch adds the new interface and just translate the call for
the old interface, without implementing new features. The goal here is
to establish the interface and to check if everyone is happy with this
API. The rest of patches are selftests to show the interface in action.
I have the following questions:

- What suggestions do you have to implement this? Start from scratch or
  reuse the most code possible?

- The interface seems correct and implements the requirements asked by you?

Those are the cool new features that this syscall should address some
day:

- Operate with variable bit size futexes, not restricted to 32:
  8, 16 and 64

- Wait on multiple futexes, using the following semantics:

  struct futex_wait {
        void *uaddr;
        unsigned long val;
        unsigned long flags;
  };

  sys_futex_waitv(struct futex_wait *waiters, unsigned int nr_waiters,
                  unsigned long flags, struct __kernel_timespec *timo);

- Have NUMA optimizations: if FUTEX_NUMA_FLAG is set, the `void *uaddr`
  argument won't be a value of type u{8, 16, 32, 64} anymore, but a struct
  containing a NUMA node hint:

  struct futex32_numa {
          u32 value __attribute__ ((aligned (8)));
          u32 hint;
  };

  struct futex64_numa {
          u64 value __attribute__ ((aligned (16)));
          u64 hint;
  };

Thanks,
        André

Changes since v1:
 - The timeout argument now uses __kernel_timespec as type
 - time32 interface was removed
 v1: https://lore.kernel.org/patchwork/cover/1255437/

[1] https://lore.kernel.org/patchwork/patch/1194339/

André Almeida (4):
  futex2: Add new futex interface
  selftests: futex: Add futex2 wake/wait test
  selftests: futex: Add futex2 timeout test
  selftests: futex: Add futex2 wouldblock test

 MAINTAINERS                                   |   2 +-
 arch/x86/entry/syscalls/syscall_32.tbl        |   2 +
 arch/x86/entry/syscalls/syscall_64.tbl        |   2 +
 include/linux/syscalls.h                      |   7 ++
 include/uapi/asm-generic/unistd.h             |   8 +-
 include/uapi/linux/futex.h                    |  10 ++
 init/Kconfig                                  |   7 ++
 kernel/Makefile                               |   1 +
 kernel/futex2.c                               |  73 ++++++++++++
 kernel/sys_ni.c                               |   4 +
 tools/include/uapi/asm-generic/unistd.h       |   7 +-
 .../selftests/futex/functional/.gitignore     |   1 +
 .../selftests/futex/functional/Makefile       |   4 +-
 .../selftests/futex/functional/futex2_wait.c  | 111 ++++++++++++++++++
 .../futex/functional/futex_wait_timeout.c     |  38 ++++--
 .../futex/functional/futex_wait_wouldblock.c  |  33 +++++-
 .../testing/selftests/futex/functional/run.sh |   3 +
 .../selftests/futex/include/futex2test.h      |  77 ++++++++++++
 18 files changed, 373 insertions(+), 17 deletions(-)
 create mode 100644 kernel/futex2.c
 create mode 100644 tools/testing/selftests/futex/functional/futex2_wait.c
 create mode 100644 tools/testing/selftests/futex/include/futex2test.h

--
2.27.0

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[RFC v2 1/4] futex2: Add new futex interface

Sourceware - libc-alpha mailing list
Add a new futex interface into the kernel, namely futex2. This first
piece of work just introduces the new interface without new feature for
now, using all mechanisms of the old interface in order to work. This
way we can properly formalize the expectations around the new design,
while being able to expand the code as we need and even in parallel
efforts if possible.

This new interface is able just to wait and wake on a 32 bits user futex.
The wait operation supports timeout with absolute values only, using
timespec64, in monotonic or realtime mode. This syscall is not compatible
with ABIs that have timesize as 32 bits, only the ones that support 64
bits timesize. The code can be found in my git tree[1].

The design of this syscall was based on the discussion following the
"futex: Implement mechanism to wait on any of several futexes" patch[2].

In order to test the code, the glibc 2.31 low level futex code was
modified to use the new syscall. It's possible to find the code here[3].
After running the tests of glibc (`make check subdir=nptl`), only 26
tests of 370 didn't passed, and since they are all related to FUTEX_PI,
which isn't implemented in the new interface, those failures were expected.
All kernel selftests were successful.

[1] https://gitlab.collabora.com/tonyk/linux/-/commits/futex2
[2] https://lore.kernel.org/patchwork/patch/1194339/
[3] https://gitlab.collabora.com/tonyk/glibc/-/commits/futex2

Signed-off-by: André Almeida <[hidden email]>
---
 MAINTAINERS                            |  2 +-
 arch/x86/entry/syscalls/syscall_32.tbl |  2 +
 arch/x86/entry/syscalls/syscall_64.tbl |  2 +
 include/linux/syscalls.h               |  7 +++
 include/uapi/asm-generic/unistd.h      |  8 ++-
 include/uapi/linux/futex.h             | 10 ++++
 init/Kconfig                           |  7 +++
 kernel/Makefile                        |  1 +
 kernel/futex2.c                        | 73 ++++++++++++++++++++++++++
 kernel/sys_ni.c                        |  4 ++
 10 files changed, 114 insertions(+), 2 deletions(-)
 create mode 100644 kernel/futex2.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 68f21d46614c..b4f60532317b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7104,7 +7104,7 @@ F: Documentation/locking/*futex*
 F: include/asm-generic/futex.h
 F: include/linux/futex.h
 F: include/uapi/linux/futex.h
-F: kernel/futex.c
+F: kernel/futex*
 F: tools/perf/bench/futex*
 F: Documentation/locking/*futex*
 
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index d8f8a1a69ed1..f7a263f1ca98 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -443,3 +443,5 @@
 437 i386 openat2 sys_openat2
 438 i386 pidfd_getfd sys_pidfd_getfd
 439 i386 faccessat2 sys_faccessat2
+440 i386 futex_wait sys_futex_wait
+441 i386 futex_wake sys_futex_wake
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 78847b32e137..310eb1fd9a1e 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -360,6 +360,8 @@
 437 common openat2 sys_openat2
 438 common pidfd_getfd sys_pidfd_getfd
 439 common faccessat2 sys_faccessat2
+440 common futex_wait sys_futex_wait
+441 common futex_wake sys_futex_wake
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 7c354c2955f5..04fe9f20f522 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -588,6 +588,13 @@ asmlinkage long sys_get_robust_list(int pid,
 asmlinkage long sys_set_robust_list(struct robust_list_head __user *head,
     size_t len);
 
+/* kernel/futex2.c */
+asmlinkage long sys_futex_wait(void __user *uaddr, unsigned long val,
+       unsigned long flags,
+       struct __kernel_timespec __user __user *timo);
+asmlinkage long sys_futex_wake(void __user *uaddr, unsigned long nr_wake,
+       unsigned long 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 f4a01305d9a6..e3e03350ae76 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -858,8 +858,14 @@ __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
 #define __NR_faccessat2 439
 __SYSCALL(__NR_faccessat2, sys_faccessat2)
 
+#define __NR_futex_wait 440
+__SYSCALL(__NR_futex_wait, sys_futex_wait)
+
+#define __NR_futex_wake 441
+__SYSCALL(__NR_futex_wake, sys_futex_wake)
+
 #undef __NR_syscalls
-#define __NR_syscalls 440
+#define __NR_syscalls 442
 
 /*
  * 32 bit systems traditionally used different
diff --git a/include/uapi/linux/futex.h b/include/uapi/linux/futex.h
index a89eb0accd5e..1e67778690eb 100644
--- a/include/uapi/linux/futex.h
+++ b/include/uapi/linux/futex.h
@@ -41,6 +41,16 @@
 #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
+#if __BITS_PER_LONG == 64 || defined(__x86_64__)
+# define FUTEX_64 3
+#endif
+
+#define FUTEX_SIZE_MASK 0x3
+
 /*
  * Support for robust futexes: the kernel cleans up held futexes at
  * thread exit time.
diff --git a/init/Kconfig b/init/Kconfig
index a46aa8f3174d..166dec71dae4 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1493,6 +1493,13 @@ config FUTEX
   support for "fast userspace mutexes".  The resulting kernel may not
   run glibc-based applications correctly.
 
+config FUTEX2
+ bool "Enable futex2 support" if EXPERT
+ depends on FUTEX
+ default n
+ help
+  Experimental support for futex2 interface.
+
 config FUTEX_PI
  bool
  depends on FUTEX && RT_MUTEXES
diff --git a/kernel/Makefile b/kernel/Makefile
index f3218bc5ec69..7698187de0b0 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -55,6 +55,7 @@ obj-$(CONFIG_PROFILING) += profile.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
 obj-y += time/
 obj-$(CONFIG_FUTEX) += futex.o
+obj-$(CONFIG_FUTEX2) += futex2.o
 obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
 obj-$(CONFIG_SMP) += smp.o
 ifneq ($(CONFIG_SMP),y)
diff --git a/kernel/futex2.c b/kernel/futex2.c
new file mode 100644
index 000000000000..b87a10ba7c01
--- /dev/null
+++ b/kernel/futex2.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * futex2 system call interface by André Almeida <[hidden email]>
+ *
+ * Copyright 2020 Collabora Ltd.
+ */
+
+#include <linux/syscalls.h>
+
+#include <asm/futex.h>
+
+/*
+ * Set of flags that futex2 operates. If we got something that is not in this
+ * set, it can be a unsupported futex1 operation like BITSET or PI, so we
+ * refuse to accept
+ */
+#define FUTEX2_MASK (FUTEX_SIZE_MASK | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
+
+/**
+ * sys_futex_wait: Wait on a futex address if (*uaddr) == val
+ * @uaddr: User address of futex
+ * @val:   Expected value of futex
+ * @flags: Checks if futex is private, the size of futex and the clockid
+ * @timo:  Optional absolute timeout. Supports only 64bit time.
+ */
+SYSCALL_DEFINE4(futex_wait, void __user *, uaddr, unsigned long, val,
+ unsigned long, flags, struct __kernel_timespec __user *, timo)
+{
+ int op = FUTEX_WAIT | (flags & (FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME));
+ unsigned int size = flags & FUTEX_SIZE_MASK;
+ struct timespec64 ts;
+ ktime_t aux, *kt = NULL;
+
+ if (flags & ~FUTEX2_MASK)
+ return -EINVAL;
+
+ if (size != FUTEX_32)
+ return -EINVAL;
+
+ if (timo) {
+ if (get_timespec64(&ts, timo))
+ return -EFAULT;
+
+ if (!timespec64_valid(&ts))
+ return -EINVAL;
+
+ aux = timespec64_to_ktime(ts);
+ kt = &aux;
+ }
+
+ return do_futex(uaddr, op, val, kt, NULL, 0, 0);
+}
+
+/**
+ * sys_futex_wake: Wake a number of futexes waiting in an address
+ * @uaddr:   Address of futex to be woken up
+ * @nr_wake: Number of futexes to be woken up
+ * @flags:   Checks if futex is private and the size of futex
+ */
+SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake,
+ unsigned long, flags)
+{
+ int op = FUTEX_WAKE | (flags & (FUTEX_PRIVATE_FLAG));
+ unsigned int size = flags & FUTEX_SIZE_MASK;
+
+ if (flags & ~FUTEX2_MASK)
+ return -EINVAL;
+
+ if (size != FUTEX_32)
+ return -EINVAL;
+
+ return do_futex(uaddr, op, nr_wake, NULL, NULL, 0, 0);
+}
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 3b69a560a7ac..f04965322a2e 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -148,6 +148,10 @@ COND_SYSCALL_COMPAT(set_robust_list);
 COND_SYSCALL(get_robust_list);
 COND_SYSCALL_COMPAT(get_robust_list);
 
+/* kernel/futex2.c */
+COND_SYSCALL(futex_wait);
+COND_SYSCALL(futex_wake);
+
 /* kernel/hrtimer.c */
 
 /* kernel/itimer.c */
--
2.27.0

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[RFC v2 2/4] selftests: futex: Add futex2 wake/wait test

Sourceware - libc-alpha mailing list
In reply to this post by Sourceware - libc-alpha mailing list
Add a simple test to test wake/wait mechanism using futex2 interface.
Create helper files so more tests can evaluate futex2. While 32bit ABIs
from glibc aren't able to use 64 bit sized time variables, add a
temporary workaround that implements the required types and calls the
appropriated syscalls, since futex2 doesn't supports 32 bit sized time.

Signed-off-by: André Almeida <[hidden email]>
---
 tools/include/uapi/asm-generic/unistd.h       |   7 +-
 .../selftests/futex/functional/.gitignore     |   1 +
 .../selftests/futex/functional/Makefile       |   4 +-
 .../selftests/futex/functional/futex2_wait.c  | 111 ++++++++++++++++++
 .../testing/selftests/futex/functional/run.sh |   3 +
 .../selftests/futex/include/futex2test.h      |  77 ++++++++++++
 6 files changed, 201 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/futex/functional/futex2_wait.c
 create mode 100644 tools/testing/selftests/futex/include/futex2test.h

diff --git a/tools/include/uapi/asm-generic/unistd.h b/tools/include/uapi/asm-generic/unistd.h
index 3a3201e4618e..40fbf4ce49ff 100644
--- a/tools/include/uapi/asm-generic/unistd.h
+++ b/tools/include/uapi/asm-generic/unistd.h
@@ -856,8 +856,13 @@ __SYSCALL(__NR_openat2, sys_openat2)
 #define __NR_pidfd_getfd 438
 __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
 
+#define __NR_futex_wait 440
+__SYSCALL(__NR_futex_wait, sys_futex_wait)
+#define __NR_futex_wake 441
+__SYSCALL(__NR_futex_wake, sys_futex_wake)
+
 #undef __NR_syscalls
-#define __NR_syscalls 439
+#define __NR_syscalls 442
 
 /*
  * 32 bit systems traditionally used different
diff --git a/tools/testing/selftests/futex/functional/.gitignore b/tools/testing/selftests/futex/functional/.gitignore
index 0efcd494daab..d61f1df94360 100644
--- a/tools/testing/selftests/futex/functional/.gitignore
+++ b/tools/testing/selftests/futex/functional/.gitignore
@@ -6,3 +6,4 @@ futex_wait_private_mapped_file
 futex_wait_timeout
 futex_wait_uninitialized_heap
 futex_wait_wouldblock
+futex2_wait
diff --git a/tools/testing/selftests/futex/functional/Makefile b/tools/testing/selftests/futex/functional/Makefile
index 23207829ec75..7142a94a7ac3 100644
--- a/tools/testing/selftests/futex/functional/Makefile
+++ b/tools/testing/selftests/futex/functional/Makefile
@@ -5,6 +5,7 @@ LDLIBS := -lpthread -lrt
 
 HEADERS := \
  ../include/futextest.h \
+ ../include/futex2test.h \
  ../include/atomic.h \
  ../include/logging.h
 TEST_GEN_FILES := \
@@ -14,7 +15,8 @@ TEST_GEN_FILES := \
  futex_requeue_pi_signal_restart \
  futex_requeue_pi_mismatched_ops \
  futex_wait_uninitialized_heap \
- futex_wait_private_mapped_file
+ futex_wait_private_mapped_file \
+ futex2_wait
 
 TEST_PROGS := run.sh
 
diff --git a/tools/testing/selftests/futex/functional/futex2_wait.c b/tools/testing/selftests/futex/functional/futex2_wait.c
new file mode 100644
index 000000000000..752ed26803b3
--- /dev/null
+++ b/tools/testing/selftests/futex/functional/futex2_wait.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/******************************************************************************
+ *
+ *   Copyright Collabora Ltd., 2020
+ *
+ * DESCRIPTION
+ * Test wait/wake mechanism of futex2, using 32bit sized futexes.
+ *
+ * AUTHOR
+ * André Almeida <[hidden email]>
+ *
+ * HISTORY
+ *      2020-Jul-9: Initial version by André <[hidden email]>
+ *
+ *****************************************************************************/
+
+#include <errno.h>
+#include <error.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <pthread.h>
+#include "futex2test.h"
+#include "logging.h"
+
+#define TEST_NAME "futex-wait-wouldblock"
+#define timeout_ns  30000000
+#define WAKE_WAIT_US 10000
+futex_t f1 = FUTEX_INITIALIZER;
+
+void usage(char *prog)
+{
+ printf("Usage: %s\n", prog);
+ printf("  -c Use color\n");
+ printf("  -h Display this help message\n");
+ printf("  -v L Verbosity level: %d=QUIET %d=CRITICAL %d=INFO\n",
+       VQUIET, VCRITICAL, VINFO);
+}
+
+void *waiterfn(void *arg)
+{
+ struct timespec64 to64;
+
+ /* setting absolute timeout for futex2 */
+ if (gettime64(CLOCK_MONOTONIC, &to64))
+ error("gettime64 failed\n", errno);
+
+ to64.tv_nsec += timeout_ns;
+
+ if (to64.tv_nsec >= 1000000000) {
+ to64.tv_sec++;
+ to64.tv_nsec -= 1000000000;
+ }
+
+ if (futex2_wait(&f1, f1, FUTEX_PRIVATE_FLAG | FUTEX_32, &to64))
+ printf("waiter failed errno %d\n", errno);
+
+ return NULL;
+}
+
+int main(int argc, char *argv[])
+{
+ pthread_t waiter;
+ int res, ret = RET_PASS;
+ int c;
+
+ while ((c = getopt(argc, argv, "cht:v:")) != -1) {
+ switch (c) {
+ case 'c':
+ log_color(1);
+ break;
+ case 'h':
+ usage(basename(argv[0]));
+ exit(0);
+ case 'v':
+ log_verbosity(atoi(optarg));
+ break;
+ default:
+ usage(basename(argv[0]));
+ exit(1);
+ }
+ }
+
+ ksft_print_header();
+ ksft_set_plan(1);
+ ksft_print_msg("%s: Test FUTEX_WAIT\n",
+       basename(argv[0]));
+
+ info("Calling futex_wait on f1: %u @ %p with val=%u\n", f1, &f1, f1);
+
+ if (pthread_create(&waiter, NULL, waiterfn, NULL))
+ error("pthread_create failed\n", errno);
+
+ usleep(WAKE_WAIT_US);
+
+ info("Calling futex2_wake on f1: %u @ %p with val=%u\n", f1, &f1, f1);
+ res = futex2_wake(&f1, 1, FUTEX_PRIVATE_FLAG | FUTEX_32);
+ if (res != 1) {
+ ksft_test_result_fail("futex2_wake returned: %d %s\n",
+      res ? errno : res,
+      res ? strerror(errno) : "");
+ ret = RET_FAIL;
+ } else {
+ ksft_test_result_pass("futex2_wake wouldblock succeeds\n");
+ }
+
+ ksft_print_cnts();
+ return ret;
+}
diff --git a/tools/testing/selftests/futex/functional/run.sh b/tools/testing/selftests/futex/functional/run.sh
index 1acb6ace1680..3730159c865a 100755
--- a/tools/testing/selftests/futex/functional/run.sh
+++ b/tools/testing/selftests/futex/functional/run.sh
@@ -73,3 +73,6 @@ echo
 echo
 ./futex_wait_uninitialized_heap $COLOR
 ./futex_wait_private_mapped_file $COLOR
+
+echo
+./futex2_wait $COLOR
diff --git a/tools/testing/selftests/futex/include/futex2test.h b/tools/testing/selftests/futex/include/futex2test.h
new file mode 100644
index 000000000000..807b8b57fe61
--- /dev/null
+++ b/tools/testing/selftests/futex/include/futex2test.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/******************************************************************************
+ *
+ *   Copyright Collabora Ltd., 2020
+ *
+ * DESCRIPTION
+ * Futex2 library addons for old futex library
+ *
+ * AUTHOR
+ * André Almeida <[hidden email]>
+ *
+ * HISTORY
+ *      2020-Jul-9: Initial version by André <[hidden email]>
+ *
+ *****************************************************************************/
+#include "futextest.h"
+#include <stdio.h>
+
+#define NSEC_PER_SEC 1000000000L
+
+#ifndef FUTEX_8
+# define FUTEX_8 0
+#endif
+#ifndef FUTEX_16
+# define FUTEX_16 1
+#endif
+#ifndef FUTEX_32
+#define FUTEX_32 2
+#endif
+#ifdef __x86_64__
+# ifndef FUTEX_64
+#  define FUTEX_64      3
+# endif
+#endif
+
+/*
+ * - Y2038 section for 32-bit applications -
+ *
+ * Remove this when glibc is ready for y2038. Then, always compile with
+ * `-DTIME_BITS=64` or `-D__USE_TIME_BITS64`. glibc will provide both
+ * timespec64 and clock_gettime64 so we won't need to define here.
+ */
+#if defined(__i386__) || __TIMESIZE == 32
+# define NR_gettime __NR_clock_gettime64
+#else
+# define NR_gettime __NR_clock_gettime
+#endif
+
+struct timespec64 {
+ long long tv_sec; /* seconds */
+ long long tv_nsec; /* nanoseconds */
+};
+
+int gettime64(clock_t clockid, struct timespec64 *tv)
+{
+ return syscall(NR_gettime, clockid, tv);
+}
+/*
+ * - End of Y2038 section -
+ */
+
+/*
+ * wait for uaddr if (*uaddr == val)
+ */
+static inline int futex2_wait(volatile void *uaddr, unsigned long val,
+      unsigned long flags, struct timespec64 *timo)
+{
+ return syscall(__NR_futex_wait, uaddr, val, flags, timo);
+}
+
+/*
+ * wake nr futexes waiting for uaddr
+ */
+static inline int futex2_wake(volatile void *uaddr, unsigned int nr, unsigned long flags)
+{
+ return syscall(__NR_futex_wake, uaddr, nr, flags);
+}
--
2.27.0

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[RFC v2 3/4] selftests: futex: Add futex2 timeout test

Sourceware - libc-alpha mailing list
In reply to this post by Sourceware - libc-alpha mailing list
Adapt existing futex wait timeout file to test the same mechanism for
futex2.

Signed-off-by: André Almeida <[hidden email]>
---
 .../futex/functional/futex_wait_timeout.c     | 38 ++++++++++++++-----
 1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/futex/functional/futex_wait_timeout.c b/tools/testing/selftests/futex/functional/futex_wait_timeout.c
index ee55e6d389a3..d2e7ae18985b 100644
--- a/tools/testing/selftests/futex/functional/futex_wait_timeout.c
+++ b/tools/testing/selftests/futex/functional/futex_wait_timeout.c
@@ -11,6 +11,7 @@
  *
  * HISTORY
  *      2009-Nov-6: Initial version by Darren Hart <[hidden email]>
+ *      2020-Jul-9: Add futex2 test by André <[hidden email]>
  *
  *****************************************************************************/
 
@@ -20,7 +21,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
-#include "futextest.h"
+#include "futex2test.h"
 #include "logging.h"
 
 #define TEST_NAME "futex-wait-timeout"
@@ -40,7 +41,8 @@ void usage(char *prog)
 int main(int argc, char *argv[])
 {
  futex_t f1 = FUTEX_INITIALIZER;
- struct timespec to;
+ struct timespec to = {.tv_sec = 0, .tv_nsec = timeout_ns};
+ struct timespec64 to64;
  int res, ret = RET_PASS;
  int c;
 
@@ -65,22 +67,40 @@ int main(int argc, char *argv[])
  }
 
  ksft_print_header();
- ksft_set_plan(1);
+ ksft_set_plan(2);
  ksft_print_msg("%s: Block on a futex and wait for timeout\n",
        basename(argv[0]));
  ksft_print_msg("\tArguments: timeout=%ldns\n", timeout_ns);
 
- /* initialize timeout */
- to.tv_sec = 0;
- to.tv_nsec = timeout_ns;
-
  info("Calling futex_wait on f1: %u @ %p\n", f1, &f1);
  res = futex_wait(&f1, f1, &to, FUTEX_PRIVATE_FLAG);
  if (!res || errno != ETIMEDOUT) {
- fail("futex_wait returned %d\n", ret < 0 ? errno : ret);
+ ksft_test_result_fail("futex_wait returned %d\n", ret < 0 ? errno : ret);
+ ret = RET_FAIL;
+ } else {
+ ksft_test_result_pass("futex_wait timeout succeeds\n");
+ }
+
+ /* setting absolute timeout for futex2 */
+ if (gettime64(CLOCK_MONOTONIC, &to64))
+ error("gettime64 failed\n", errno);
+
+ to64.tv_nsec += timeout_ns;
+
+ if (to64.tv_nsec >= 1000000000) {
+ to64.tv_sec++;
+ to64.tv_nsec -= 1000000000;
+ }
+
+ info("Calling futex2_wait on f1: %u @ %p\n", f1, &f1);
+ res = futex2_wait(&f1, f1, FUTEX_PRIVATE_FLAG | FUTEX_32, &to64);
+ if (!res || errno != ETIMEDOUT) {
+ ksft_test_result_fail("futex2_wait returned %d\n", ret < 0 ? errno : ret);
  ret = RET_FAIL;
+ } else {
+ ksft_test_result_pass("futex2_wait timeout succeeds\n");
  }
 
- print_result(TEST_NAME, ret);
+ ksft_print_cnts();
  return ret;
 }
--
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[RFC v2 4/4] selftests: futex: Add futex2 wouldblock test

Sourceware - libc-alpha mailing list
In reply to this post by Sourceware - libc-alpha mailing list
Adapt existing futex wait wouldblock file to test the same mechanism for
futex2.

Signed-off-by: André Almeida <[hidden email]>
---
 .../futex/functional/futex_wait_wouldblock.c  | 33 ++++++++++++++++---
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/futex/functional/futex_wait_wouldblock.c b/tools/testing/selftests/futex/functional/futex_wait_wouldblock.c
index 0ae390ff8164..8187f0754cd2 100644
--- a/tools/testing/selftests/futex/functional/futex_wait_wouldblock.c
+++ b/tools/testing/selftests/futex/functional/futex_wait_wouldblock.c
@@ -12,6 +12,7 @@
  *
  * HISTORY
  *      2009-Nov-14: Initial version by Gowrishankar <[hidden email]>
+ *      2020-Jul-9: Add futex2 test by André <[hidden email]>
  *
  *****************************************************************************/
 
@@ -21,7 +22,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
-#include "futextest.h"
+#include "futex2test.h"
 #include "logging.h"
 
 #define TEST_NAME "futex-wait-wouldblock"
@@ -39,6 +40,7 @@ void usage(char *prog)
 int main(int argc, char *argv[])
 {
  struct timespec to = {.tv_sec = 0, .tv_nsec = timeout_ns};
+ struct timespec64 to64;
  futex_t f1 = FUTEX_INITIALIZER;
  int res, ret = RET_PASS;
  int c;
@@ -61,18 +63,41 @@ int main(int argc, char *argv[])
  }
 
  ksft_print_header();
- ksft_set_plan(1);
+ ksft_set_plan(2);
  ksft_print_msg("%s: Test the unexpected futex value in FUTEX_WAIT\n",
        basename(argv[0]));
 
  info("Calling futex_wait on f1: %u @ %p with val=%u\n", f1, &f1, f1+1);
  res = futex_wait(&f1, f1+1, &to, FUTEX_PRIVATE_FLAG);
  if (!res || errno != EWOULDBLOCK) {
- fail("futex_wait returned: %d %s\n",
+ ksft_test_result_fail("futex_wait returned: %d %s\n",
      res ? errno : res, res ? strerror(errno) : "");
  ret = RET_FAIL;
+ } else {
+ ksft_test_result_pass("futex_wait wouldblock succeeds\n");
  }
 
- print_result(TEST_NAME, ret);
+ /* setting absolute timeout for futex2 */
+ if (gettime64(CLOCK_MONOTONIC, &to64))
+ error("gettime64 failed\n", errno);
+
+ to64.tv_nsec += timeout_ns;
+
+ if (to64.tv_nsec >= 1000000000) {
+ to64.tv_sec++;
+ to64.tv_nsec -= 1000000000;
+ }
+
+ info("Calling futex2_wait on f1: %u @ %p with val=%u\n", f1, &f1, f1+1);
+ res = futex2_wait(&f1, f1+1, FUTEX_PRIVATE_FLAG | FUTEX_32, &to64);
+ if (!res || errno != EWOULDBLOCK) {
+ ksft_test_result_fail("futex2_wait returned: %d %s\n",
+     res ? errno : res, res ? strerror(errno) : "");
+ ret = RET_FAIL;
+ } else {
+ ksft_test_result_pass("futex2_wait wouldblock succeeds\n");
+ }
+
+ ksft_print_cnts();
  return ret;
 }
--
2.27.0

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Re: [RFC v2 1/4] futex2: Add new futex interface

Randy Dunlap
In reply to this post by Sourceware - libc-alpha mailing list
Hi,

On 7/9/20 10:59 AM, André Almeida wrote:

>
>
> diff --git a/kernel/futex2.c b/kernel/futex2.c
> new file mode 100644
> index 000000000000..b87a10ba7c01
> --- /dev/null
> +++ b/kernel/futex2.c
> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * futex2 system call interface by André Almeida <[hidden email]>
> + *
> + * Copyright 2020 Collabora Ltd.
> + */
> +
> +#include <linux/syscalls.h>
> +
> +#include <asm/futex.h>
> +
> +/*
> + * Set of flags that futex2 operates. If we got something that is not in this
> + * set, it can be a unsupported futex1 operation like BITSET or PI, so we
> + * refuse to accept
> + */
> +#define FUTEX2_MASK (FUTEX_SIZE_MASK | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
> +
> +/**
> + * sys_futex_wait: Wait on a futex address if (*uaddr) == val

Function name line should use - as separator, not :, so
 * sys_futex_wait - Wait on a futex address if (*uaddr) == val

> + * @uaddr: User address of futex
> + * @val:   Expected value of futex
> + * @flags: Checks if futex is private, the size of futex and the clockid
> + * @timo:  Optional absolute timeout. Supports only 64bit time.
> + */
> +SYSCALL_DEFINE4(futex_wait, void __user *, uaddr, unsigned long, val,
> + unsigned long, flags, struct __kernel_timespec __user *, timo)
> +{
  ...
> +}
> +
> +/**
> + * sys_futex_wake: Wake a number of futexes waiting in an address

Same here:
 * sys_futex_wake - Wake a number of futexes waiting in an address

or could it be "on an address":
 * sys_futex_wake - Wake a number of futexes waiting on an address

> + * @uaddr:   Address of futex to be woken up
> + * @nr_wake: Number of futexes to be woken up
> + * @flags:   Checks if futex is private and the size of futex
> + */
> +SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake,
> + unsigned long, flags)
> +{


thanks.
--
~Randy

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Re: [RFC v2 1/4] futex2: Add new futex interface

Sourceware - libc-alpha mailing list
Hello,

On 7/9/20 9:09 PM, Randy Dunlap wrote:

> Hi,
>
> On 7/9/20 10:59 AM, André Almeida wrote:
>>
>>
>> diff --git a/kernel/futex2.c b/kernel/futex2.c
>> new file mode 100644
>> index 000000000000..b87a10ba7c01
>> --- /dev/null
>> +++ b/kernel/futex2.c
>> @@ -0,0 +1,73 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * futex2 system call interface by André Almeida <[hidden email]>
>> + *
>> + * Copyright 2020 Collabora Ltd.
>> + */
>> +
>> +#include <linux/syscalls.h>
>> +
>> +#include <asm/futex.h>
>> +
>> +/*
>> + * Set of flags that futex2 operates. If we got something that is not in this
>> + * set, it can be a unsupported futex1 operation like BITSET or PI, so we
>> + * refuse to accept
>> + */
>> +#define FUTEX2_MASK (FUTEX_SIZE_MASK | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
>> +
>> +/**
>> + * sys_futex_wait: Wait on a futex address if (*uaddr) == val
>
> Function name line should use - as separator, not :, so
>  * sys_futex_wait - Wait on a futex address if (*uaddr) == val
>
>> + * @uaddr: User address of futex
>> + * @val:   Expected value of futex
>> + * @flags: Checks if futex is private, the size of futex and the clockid
>> + * @timo:  Optional absolute timeout. Supports only 64bit time.
>> + */
>> +SYSCALL_DEFINE4(futex_wait, void __user *, uaddr, unsigned long, val,
>> + unsigned long, flags, struct __kernel_timespec __user *, timo)
>> +{
>   ...
>> +}
>> +
>> +/**
>> + * sys_futex_wake: Wake a number of futexes waiting in an address
>
> Same here:
>  * sys_futex_wake - Wake a number of futexes waiting in an address
>
> or could it be "on an address":
>  * sys_futex_wake - Wake a number of futexes waiting on an address
>
>> + * @uaddr:   Address of futex to be woken up
>> + * @nr_wake: Number of futexes to be woken up
>> + * @flags:   Checks if futex is private and the size of futex
>> + */
>> +SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake,
>> + unsigned long, flags)
>> +{
>

Both changes applied for v3, thanks for the feedback.

>
> thanks.
>

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Re: [RFC v2 0/4] futex2: Add new futex interface

Sourceware - libc-alpha mailing list
In reply to this post by Sourceware - libc-alpha mailing list
Hello.

On 09.07.2020 19:59, André Almeida wrote:

> This RFC is a followup to the previous discussion initiated from my
> last
> patch "futex: Implement mechanism to wait on any of several
> futexes"[1].
> As stated in the thread, the correct approach to move forward with the
> wait multiple operation would be to create a new syscall that would
> have
> all new cool features.
>
> The first patch adds the new interface and just translate the call for
> the old interface, without implementing new features. The goal here is
> to establish the interface and to check if everyone is happy with this
> API. The rest of patches are selftests to show the interface in action.
> I have the following questions:
>
> - What suggestions do you have to implement this? Start from scratch or
>   reuse the most code possible?
>
> - The interface seems correct and implements the requirements asked by
> you?
>
> Those are the cool new features that this syscall should address some
> day:
>
> - Operate with variable bit size futexes, not restricted to 32:
>   8, 16 and 64
>
> - Wait on multiple futexes, using the following semantics:
>
>   struct futex_wait {
> void *uaddr;
> unsigned long val;
> unsigned long flags;
>   };
>
>   sys_futex_waitv(struct futex_wait *waiters, unsigned int nr_waiters,
>  unsigned long flags, struct __kernel_timespec *timo);
>
> - Have NUMA optimizations: if FUTEX_NUMA_FLAG is set, the `void *uaddr`
>   argument won't be a value of type u{8, 16, 32, 64} anymore, but a
> struct
>   containing a NUMA node hint:
>
>   struct futex32_numa {
>  u32 value __attribute__ ((aligned (8)));
>  u32 hint;
>   };
>
>   struct futex64_numa {
>  u64 value __attribute__ ((aligned (16)));
>  u64 hint;
>   };
>
> Thanks,
> André
>
> Changes since v1:
>  - The timeout argument now uses __kernel_timespec as type
>  - time32 interface was removed
>  v1: https://lore.kernel.org/patchwork/cover/1255437/
>
> [1] https://lore.kernel.org/patchwork/patch/1194339/
>
> André Almeida (4):
>   futex2: Add new futex interface
>   selftests: futex: Add futex2 wake/wait test
>   selftests: futex: Add futex2 timeout test
>   selftests: futex: Add futex2 wouldblock test
>
>  MAINTAINERS                                   |   2 +-
>  arch/x86/entry/syscalls/syscall_32.tbl        |   2 +
>  arch/x86/entry/syscalls/syscall_64.tbl        |   2 +
>  include/linux/syscalls.h                      |   7 ++
>  include/uapi/asm-generic/unistd.h             |   8 +-
>  include/uapi/linux/futex.h                    |  10 ++
>  init/Kconfig                                  |   7 ++
>  kernel/Makefile                               |   1 +
>  kernel/futex2.c                               |  73 ++++++++++++
>  kernel/sys_ni.c                               |   4 +
>  tools/include/uapi/asm-generic/unistd.h       |   7 +-
>  .../selftests/futex/functional/.gitignore     |   1 +
>  .../selftests/futex/functional/Makefile       |   4 +-
>  .../selftests/futex/functional/futex2_wait.c  | 111 ++++++++++++++++++
>  .../futex/functional/futex_wait_timeout.c     |  38 ++++--
>  .../futex/functional/futex_wait_wouldblock.c  |  33 +++++-
>  .../testing/selftests/futex/functional/run.sh |   3 +
>  .../selftests/futex/include/futex2test.h      |  77 ++++++++++++
>  18 files changed, 373 insertions(+), 17 deletions(-)
>  create mode 100644 kernel/futex2.c
>  create mode 100644
> tools/testing/selftests/futex/functional/futex2_wait.c
>  create mode 100644 tools/testing/selftests/futex/include/futex2test.h

What branch/tag this submission is based on please? It seems it is not a
5.8 but rather 5.7 since the second patch misses faccessat2() syscall
and fails to be applied cleanly.

Thanks.

--
   Oleksandr Natalenko (post-factum)
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Re: [RFC v2 0/4] futex2: Add new futex interface

Sourceware - libc-alpha mailing list
Hi

On 7/10/20 10:23 AM, Oleksandr Natalenko wrote:

> Hello.
>
> On 09.07.2020 19:59, André Almeida wrote:
>> This RFC is a followup to the previous discussion initiated from my last
>> patch "futex: Implement mechanism to wait on any of several futexes"[1].
>> As stated in the thread, the correct approach to move forward with the
>> wait multiple operation would be to create a new syscall that would have
>> all new cool features.
>>
>> The first patch adds the new interface and just translate the call for
>> the old interface, without implementing new features. The goal here is
>> to establish the interface and to check if everyone is happy with this
>> API. The rest of patches are selftests to show the interface in action.
>> I have the following questions:
>>
>> - What suggestions do you have to implement this? Start from scratch or
>>   reuse the most code possible?
>>
>> - The interface seems correct and implements the requirements asked by
>> you?
>>
>> Those are the cool new features that this syscall should address some
>> day:
>>
>> - Operate with variable bit size futexes, not restricted to 32:
>>   8, 16 and 64
>>
>> - Wait on multiple futexes, using the following semantics:
>>
>>   struct futex_wait {
>>     void *uaddr;
>>     unsigned long val;
>>     unsigned long flags;
>>   };
>>
>>   sys_futex_waitv(struct futex_wait *waiters, unsigned int nr_waiters,
>>           unsigned long flags, struct __kernel_timespec *timo);
>>
>> - Have NUMA optimizations: if FUTEX_NUMA_FLAG is set, the `void *uaddr`
>>   argument won't be a value of type u{8, 16, 32, 64} anymore, but a
>> struct
>>   containing a NUMA node hint:
>>
>>   struct futex32_numa {
>>       u32 value __attribute__ ((aligned (8)));
>>       u32 hint;
>>   };
>>
>>   struct futex64_numa {
>>       u64 value __attribute__ ((aligned (16)));
>>       u64 hint;
>>   };
>>
>> Thanks,
>>     André
>>
>> Changes since v1:
>>  - The timeout argument now uses __kernel_timespec as type
>>  - time32 interface was removed
>>  v1: https://lore.kernel.org/patchwork/cover/1255437/
>>
>> [1] https://lore.kernel.org/patchwork/patch/1194339/
>>
>> André Almeida (4):
>>   futex2: Add new futex interface
>>   selftests: futex: Add futex2 wake/wait test
>>   selftests: futex: Add futex2 timeout test
>>   selftests: futex: Add futex2 wouldblock test
>>
>>  MAINTAINERS                                   |   2 +-
>>  arch/x86/entry/syscalls/syscall_32.tbl        |   2 +
>>  arch/x86/entry/syscalls/syscall_64.tbl        |   2 +
>>  include/linux/syscalls.h                      |   7 ++
>>  include/uapi/asm-generic/unistd.h             |   8 +-
>>  include/uapi/linux/futex.h                    |  10 ++
>>  init/Kconfig                                  |   7 ++
>>  kernel/Makefile                               |   1 +
>>  kernel/futex2.c                               |  73 ++++++++++++
>>  kernel/sys_ni.c                               |   4 +
>>  tools/include/uapi/asm-generic/unistd.h       |   7 +-
>>  .../selftests/futex/functional/.gitignore     |   1 +
>>  .../selftests/futex/functional/Makefile       |   4 +-
>>  .../selftests/futex/functional/futex2_wait.c  | 111 ++++++++++++++++++
>>  .../futex/functional/futex_wait_timeout.c     |  38 ++++--
>>  .../futex/functional/futex_wait_wouldblock.c  |  33 +++++-
>>  .../testing/selftests/futex/functional/run.sh |   3 +
>>  .../selftests/futex/include/futex2test.h      |  77 ++++++++++++
>>  18 files changed, 373 insertions(+), 17 deletions(-)
>>  create mode 100644 kernel/futex2.c
>>  create mode 100644
>> tools/testing/selftests/futex/functional/futex2_wait.c
>>  create mode 100644 tools/testing/selftests/futex/include/futex2test.h
>
> What branch/tag this submission is based on please? It seems it is not a
> 5.8 but rather 5.7 since the second patch misses faccessat2() syscall
> and fails to be applied cleanly.
>

As stated in MAINTAINERS[1], this submission is based on locking/core
branch from tip/tip[2] tree. The most updated release tag in this tree
is v5.8-rc1. My patches applied on top of locking/core are available in
my tree: https://gitlab.collabora.com/tonyk/linux/-/commits/futex2

According to 6c3c184fc420 ("tools headers API: Update faccessat2
affected files"), it seems that `faccessat2` entry at
`tools/include/uapi/asm-generic/unistd.h` was added after the syscall
was merged, so that's why 5.8-rc1 misses the syscall in this specific
file. Rebasing locking/core in 5.8-rc2 or above will fix that.

> Thanks.
>

Thanks,
        André

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/MAINTAINERS?h=v5.8-rc4#n7102

[2]
https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=locking/core