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

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Message-ID: <87fs8x4c8k.ffs@tglx>
Date:   Tue, 18 Apr 2023 14:16:11 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH RFC] preempt: Put preempt_enable() within an
 instrumentation*() section.

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