Re: [RFC PATCH 01/22] kernel/entry/common: Move syscall_enter_from_user_mode_work() out of header

[K Prateek Nayak]

Hello Peter,

Thank you for taking a look.

On 2/20/2025 4:13 PM, Peter Zijlstra wrote:
> On Thu, Feb 20, 2025 at 09:32:36AM +0000, K Prateek Nayak wrote:
> > Retain the prototype of syscall_enter_from_user_mode_work() in
> > linux/entry-common.h and move the function definition to
> > kernel/entry/common.c in preparation to notify the scheduler of task
> > entering and exiting kernel mode for syscall. The two architectures that
> > use it directly (x86, s390) and the four that call it via
> > syscall_enter_from_user_mode() (x86, riscv, loongarch, s390) end up
> > selecting GENERIC_ENTRY, hence, no functional changes are intended.
> >
> > [..snip..]
> >
> > @@ -79,6 +79,16 @@ noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs)
> >   	instrumentation_end();
> >   }
> >   
> > +__always_inline long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall)
> > +{
> > +	unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
> > +
> > +	if (work & SYSCALL_WORK_ENTER)
> > +		syscall = syscall_trace_enter(regs, syscall, work);
> > +
> > +	return syscall;
> > +}
> > +
> >   /* Workaround to allow gradual conversion of architecture code */
> >   void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
>
> This breaks s390. While you retain an external linkage, the function
> looses the noinstr tag that's needed for correctness.
>
> Also, extern __always_inline is flaky as heck. Please don't do this.

Noted! I'll try to find another way around this.

--
Thanks and Regards,
Prateek