linux-kernel - Re: [patch V3 01/23] rcu: Dont acquire lock in NMI handler in rcu_nmi_enter

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Date:   Tue, 24 Mar 2020 16:37:55 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Paul McKenney <paulmck@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [patch V3 01/23] rcu: Dont acquire lock in NMI handler in
 rcu_nmi_enter_common()

On Fri, Mar 20, 2020 at 06:59:57PM +0100, Thomas Gleixner wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> The rcu_nmi_enter_common() function can be invoked both in interrupt
> and NMI handlers.  If it is invoked from process context (as opposed
> to userspace or idle context) on a nohz_full CPU, it might acquire the
> CPU's leaf rcu_node structure's ->lock.  Because this lock is held only
> with interrupts disabled, this is safe from an interrupt handler, but
> doing so from an NMI handler can result in self-deadlock.
> 
> This commit therefore adds "irq" to the "if" condition so as to only
> acquire the ->lock from irq handlers or process context, never from
> an NMI handler.
> 
> Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering")
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> Link: https://lkml.kernel.org/r/20200313024046.27622-1-paulmck@kernel.org

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>