Re: [PATCH RFC] preempt: Put preempt_enable() within an instrumentation*() section.

[Thomas Gleixner]

On Thu, Mar 09 2023 at 08:27, Sebastian Andrzej Siewior wrote:
> Callers of preempt_enable() can be within an noinstr section leading to:
> | vmlinux.o: warning: objtool: native_sched_clock+0x97: call to preempt_schedule_notrace_thunk() leaves .noinstr.text section
> | vmlinux.o: warning: objtool: kvm_clock_read+0x22: call to preempt_schedule_notrace_thunk() leaves .noinstr.text section
> | vmlinux.o: warning: objtool: local_clock+0xb4: call to preempt_schedule_notrace_thunk() leaves .noinstr.text section

> | vmlinux.o: warning: objtool: enter_from_user_mode+0xea: call to preempt_schedule_thunk() leaves .noinstr.text section
> | vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x140: call to preempt_schedule_thunk() leaves .noinstr.text section
> | vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0xf2: call to preempt_schedule_thunk() leaves .noinstr.text section
> | vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0xea: call to preempt_schedule_thunk() leaves .noinstr.text section 

I'm confused where this preempt_enable is in those
*_enter_from_user_mode() functions.

Kernel config and compiler version please.

>  #define preempt_enable() \
>  do { \
>  	barrier(); \
> -	if (unlikely(preempt_count_dec_and_test())) \
> +	if (unlikely(preempt_count_dec_and_test())) { \
> +		instrumentation_begin(); \
>  		__preempt_schedule(); \
> +		instrumentation_end(); \
> +	} \
>  } while (0)

This would paper over a misplaced preempt_disable/enable() pair in
noinstr code. I'm not really happy about that.

Thanks,

        tglx