linux-kernel - Re: [PATCH RFC V3 6/9] x86/entry: Pass irqentry_state

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Message-ID: <20201016114510.GO2611@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Oct 2020 13:45:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     ira.weiny@...el.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V3 6/9] x86/entry: Pass irqentry_state_t by reference

On Fri, Oct 09, 2020 at 12:42:55PM -0700, ira.weiny@...el.com wrote:
> -noinstr bool idtentry_enter_nmi(struct pt_regs *regs)
> +noinstr void idtentry_enter_nmi(struct pt_regs *regs, irqentry_state_t *irq_state)
>  {
> -	bool irq_state = lockdep_hardirqs_enabled();
> +	irq_state->exit_rcu = lockdep_hardirqs_enabled();
>  
>  	__nmi_enter();
>  	lockdep_hardirqs_off(CALLER_ADDR0);
> @@ -222,15 +222,13 @@ noinstr bool idtentry_enter_nmi(struct pt_regs *regs)
>  	trace_hardirqs_off_finish();
>  	ftrace_nmi_enter();
>  	instrumentation_end();
> -
> -	return irq_state;
>  }
>  
> -noinstr void idtentry_exit_nmi(struct pt_regs *regs, bool restore)
> +noinstr void idtentry_exit_nmi(struct pt_regs *regs, irqentry_state_t *irq_state)
>  {
>  	instrumentation_begin();
>  	ftrace_nmi_exit();
> -	if (restore) {
> +	if (irq_state->exit_rcu) {
>  		trace_hardirqs_on_prepare();
>  		lockdep_hardirqs_on_prepare(CALLER_ADDR0);
>  	}
> @@ -238,7 +236,7 @@ noinstr void idtentry_exit_nmi(struct pt_regs *regs, bool restore)
>  
>  	rcu_nmi_exit();
>  	lockdep_hardirq_exit();
> -	if (restore)
> +	if (irq_state->exit_rcu)
>  		lockdep_hardirqs_on(CALLER_ADDR0);
>  	__nmi_exit();
>  }

That's not nice.. The NMI path is different from the IRQ path and has a
different variable. Yes, this works, but *groan*.

Maybe union them if you want to avoid bloating the structure, but the
above makes it really hard to read.