Re: [patch V4 06/12] rseq: Implement sys_rseq_slice_yield()

["Arnd Bergmann" <arnd@arndb.de>]

On Sun, Nov 16, 2025, at 21:51, Thomas Gleixner wrote:
> Provide a new syscall which has the only purpose to yield the CPU after the
> kernel granted a time slice extension.
>
> sched_yield() is not suitable for that because it unconditionally
> schedules, but the end of the time slice extension is not required to
> schedule when the task was already preempted. This also allows to have a
> strict check for termination to catch user space invoking random syscalls
> including sched_yield() from a time slice extension region.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: linux-arch@vger.kernel.org
> ---
> V2: Use the proper name in sys_ni.c and add comment - Prateek

I checked that the syscalls are well-formed across
all architectures, which is easy here, since there
are no arguments.

Acked-by: Arnd Bergmann <arnd@arndb.de>

Two minor comments:

- Number 470 is also used in Christian Brauner's listns
  series. Obviously only one of you can claim that number.

> +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
> @@ -408,3 +408,4 @@
>  467	n32	open_tree_attr			sys_open_tree_attr
>  468	n32	file_getattr			sys_file_getattr
>  469	n32	file_setattr			sys_file_setattr
> +470	common	rseq_slice_yield		sys_rseq_slice_yield
> --- a/arch/mips/kernel/syscalls/syscall_n64.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
> @@ -384,3 +384,4 @@
>  467	n64	open_tree_attr			sys_open_tree_attr
>  468	n64	file_getattr			sys_file_getattr
>  469	n64	file_setattr			sys_file_setattr
> +470	common	rseq_slice_yield		sys_rseq_slice_yield
> --- a/arch/mips/kernel/syscalls/syscall_o32.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
> @@ -457,3 +457,4 @@
>  467	o32	open_tree_attr			sys_open_tree_attr
>  468	o32	file_getattr			sys_file_getattr
>  469	o32	file_setattr			sys_file_setattr
> +470	common	rseq_slice_yield		sys_rseq_slice_yield

- These should probably all become 'common' eventually, especially
  now that the s390 compat syscalls are out of the way, I would like
  to revisit my series that unifies the tables for syscalls over
  402 into a single source file. Until then, it's probably less
  confusing to keep the format and use n32/n64/o32 here.

     Arnd