linux-kernel - Re: [PATCH 1/2] x86/entry: Use should_resched() in idtentry_exit_cond

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Message-ID: <20200630120059.x5p6uh4hzgqrgwuo@linutronix.de>
Date:   Tue, 30 Jun 2020 14:00:59 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin " <hpa@...or.com>
Subject: Re: [PATCH 1/2] x86/entry: Use should_resched() in
 idtentry_exit_cond_resched()

On 2020-06-30 13:10:12 [+0200], Peter Zijlstra wrote:
> > --- a/arch/x86/entry/common.c
> > +++ b/arch/x86/entry/common.c
> > @@ -612,13 +612,12 @@ bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs)
> >  
> >  static void idtentry_exit_cond_resched(struct pt_regs *regs, bool may_sched)
> >  {
> > -	if (may_sched && !preempt_count()) {
> > +	if (may_sched && should_resched(0)) {
> >  		/* Sanity check RCU and thread stack */
> >  		rcu_irq_exit_check_preempt();
> >  		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
> >  			WARN_ON_ONCE(!on_thread_stack());
> 
> This was done on purpose, your change avoids hitting this WARN.
> 
> The thing is, if we could preempt (but not nessecarily have to) we want
> to validate we're on the thread stack.

Okay then.

Sebastian