linux-kernel - Re: [PATCH v2] x86/traps: Don't force in_interrupt() to return true in IST handlers

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Date:	Fri, 10 Jun 2016 14:50:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>,
	Andi Kleen <andi@...stfloor.org>, stable@...r.kernel.org,
	Alexander Kuleshov <kuleshovmail@...il.com>
Subject: Re: [PATCH v2] x86/traps: Don't force in_interrupt() to return true
 in IST handlers

On 05/24, Andy Lutomirski wrote:
>
>  void ist_enter(struct pt_regs *regs)
>  {
>  	if (user_mode(regs)) {
> @@ -109,13 +115,7 @@ void ist_enter(struct pt_regs *regs)
>  		rcu_nmi_enter();
>  	}
>  
> -	/*
> -	 * We are atomic because we're on the IST stack; or we're on
> -	 * x86_32, in which case we still shouldn't schedule; or we're
> -	 * on x86_64 and entered from user mode, in which case we're
> -	 * still atomic unless ist_begin_non_atomic is called.
> -	 */
> -	preempt_count_add(HARDIRQ_OFFSET);
> +	preempt_disable();

off-topic question,

perhaps it makes sense to remove another preempt_disable/preempt_enable_no_resched
in do_int3() and do_debug() ?

They were added by d99e1bd175f4291ddb6e62b22bb5bdbe3976389a ("x86/entry/traps: Refactor
preemption and interrupt flag handling") and afaics for no reason.

Oleg.