linux-kernel - Re: [patch V6 12/37] x86/entry: Provide idtentry_entry/exit_cond

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Message-ID: <87o8qiv135.fsf@nanos.tec.linutronix.de>
Date:   Wed, 20 May 2020 21:49:18 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     paulmck@...nel.org, Andy Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>
Subject: Re: [patch V6 12/37] x86/entry: Provide idtentry_entry/exit_cond_rcu()

"Paul E. McKenney" <paulmck@...nel.org> writes:
> On Wed, May 20, 2020 at 09:51:17AM -0700, Andy Lutomirski wrote:
>> Paul, the major change here is that if an IRQ hits normal kernel code
>> (i.e. code where RCU is watching and we're not in an EQS), the IRQ
>> won't call rcu_irq_enter() and rcu_irq_exit().  Instead it will call
>> rcu_tickle() on entry and nothing on exit.  Does that cover all the
>> bases?
>
> From an RCU viewpoint, yes, give or take my concerns about someone
> putting rcu_tickle() on entry and rcu_irq_exit() on exit.  Perhaps
> I can bring some lockdep trickery to bear.

An surplus rcu_irq_exit() should already trigger alarms today.

> But I must defer to Thomas and Peter on the non-RCU/non-NO_HZ_FULL
> portions of this.

I don't see a problem. Let me write that into actual testable patch
form.

Thanks,

        tglx