[PATCH v6 0/9] futex: Create {set,get}_robust_list2() syscalls

André Almeida
2025-11-22T05:51:15Z

Hello,

This version is a complete rewrite of the syscall (thanks Thomas for the
suggestions!).

* Use case

The use-case for the new syscalls is detailed in the last patch version:

https://lore.kernel.org/lkml/20250626-tonyk-robust_futex-v5-0-179194dbde8f@igalia.com

* The syscall interface

Documented at patches 3/9 "futex: Create set_robust_list2() syscall" and
4/9 "futex: Create get_robust_list2() syscall".

* Testing

I expanded the current robust list selftest to use the new interface,
and also ported the original syscall to use the new syscall internals,
and everything survived the tests.

* Changelog

Changes from v5:
- Complete interface rewrite, there are so many changes but the main
ones are the following points
- Array of robust lists now has a static size, allocated once during the
first usage of the list
- Now that the list of robust lists have a fixed size, I removed the
logic of having a command for creating a new index on the list. To
simplify things for everyone, userspace just need to call
set_robust_list2(head, 32-bit/64-bit type, index).
- Created get_robust_list2()
- The new code can be better integrated with the original interface
- v5: https://lore.kernel.org/r/20250626-tonyk-robust_futex-v5-0-179194dbde8f@igalia.com

Feedback is very welcomed!

---
André Almeida (9):
futex: Use explicit sizes for compat_robust_list structs
futex: Make exit_robust_list32() unconditionally available for 64-bit kernels
futex: Create set_robust_list2() syscall
futex: Create get_robust_list2() syscall
futex: Wire up set_robust_list2 syscall
futex: Wire up get_robust_list2 syscall
selftests/futex: Expand for set_robust_list2()
selftests/futex: Expand for get_robust_list2()
futex: Use new robust list API internally

arch/alpha/kernel/syscalls/syscall.tbl | 2 +
arch/arm/tools/syscall.tbl | 2 +
arch/m68k/kernel/syscalls/syscall.tbl | 2 +
arch/microblaze/kernel/syscalls/syscall.tbl | 2 +
arch/mips/kernel/syscalls/syscall_n32.tbl | 2 +
arch/mips/kernel/syscalls/syscall_n64.tbl | 2 +
arch/mips/kernel/syscalls/syscall_o32.tbl | 2 +
arch/parisc/kernel/syscalls/syscall.tbl | 2 +
arch/powerpc/kernel/syscalls/syscall.tbl | 2 +
arch/s390/kernel/syscalls/syscall.tbl | 2 +
arch/sh/kernel/syscalls/syscall.tbl | 2 +
arch/sparc/kernel/syscalls/syscall.tbl | 2 +
arch/x86/entry/syscalls/syscall_32.tbl | 2 +
arch/x86/entry/syscalls/syscall_64.tbl | 2 +
arch/xtensa/kernel/syscalls/syscall.tbl | 2 +
include/linux/compat.h | 13 +-
include/linux/futex.h | 30 +-
include/linux/sched.h | 6 +-
include/uapi/asm-generic/unistd.h | 7 +-
include/uapi/linux/futex.h | 26 ++
kernel/futex/core.c | 140 ++++--
kernel/futex/syscalls.c | 134 +++++-
kernel/sys_ni.c | 2 +
scripts/syscall.tbl | 1 +
.../selftests/futex/functional/robust_list.c | 504 +++++++++++++++++++--
25 files changed, 788 insertions(+), 105 deletions(-)
---
base-commit: c42ba5a87bdccbca11403b7ca8bad1a57b833732
change-id: 20250225-tonyk-robust_futex-60adeedac695

Best regards,
--
André Almeida <andrealmeid@igalia.com>