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
