From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD352C2BAEE for ; Fri, 13 Mar 2020 03:52:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 90870206E2 for ; Fri, 13 Mar 2020 03:52:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="e+obtGsM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726414AbgCMDwE (ORCPT ); Thu, 12 Mar 2020 23:52:04 -0400 Received: from mail-qk1-f195.google.com ([209.85.222.195]:34069 "EHLO mail-qk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbgCMDwE (ORCPT ); Thu, 12 Mar 2020 23:52:04 -0400 Received: by mail-qk1-f195.google.com with SMTP id f3so10354119qkh.1 for ; Thu, 12 Mar 2020 20:52:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ER4yQwvRL6bFJRFz9hkOSe0+qiSsIHfISgRhaLCNYXM=; b=e+obtGsMJrNM8VC93u6iDKH6pQiUVW0J+QmWSLfLGxex6nuLo6NkDpCubzWzmHBPzK a6TDmhdQpog/5B1h7Wp7OlnvTG1AIxbxkmiFzL2zYN0oUa4y5fYmZWTkdlQUH+8OW+9J c/ajjNujOlO0zF617cS5W4r8rDENWu+4SmAp0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ER4yQwvRL6bFJRFz9hkOSe0+qiSsIHfISgRhaLCNYXM=; b=MUiR5PqAskCjXv60SfEZ3KEK2nwq9meH0LK1RQAMYSltKhCwvuglzHaAq9h025wKi4 bmMpbJ486ZqqBVqw6MEXQn+bi2TDkUE9hB+fa8CN6V3YtSJ7/h3B6FNzl7wJuw9Z4Swy 9ZOic3ELu9V0tuLtQ7uMYwATxBDSFYvAAwI0/NFclXD1cXjzgELL8lKB1zaO9byrV7ao I9tFU08JY7J7xzRy1AZQ41OWOYouak522f/Y+MGjZO2p//2eV2zU5RB2RIUM0vDRLp1g prEqSJLlB5MqEqk2XwBBQ3zsZM3wb14O4BJ8tyqyMK1wv5PWGqLlnrUd/VmVMjwgU1CP Rb3w== X-Gm-Message-State: ANhLgQ1U+KVnBXKeZpHqt+1TDSL568FJEZAOhYocMPcGDaxnZa/8fBLJ lxpQZiSF2C+A5LEcdWb+NIaiIg== X-Google-Smtp-Source: ADFU+vv/2QzBA+A05d6GNkRKznzI55wUVWpJfeZUpugFkkQpSNLqAzNrGDsZ29ruZPq0GJrQvyyahw== X-Received: by 2002:a37:a6d4:: with SMTP id p203mr11452462qke.184.1584071522866; Thu, 12 Mar 2020 20:52:02 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id 131sm28733662qkl.86.2020.03.12.20.52.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Mar 2020 20:52:02 -0700 (PDT) Date: Thu, 12 Mar 2020 23:52:01 -0400 From: Joel Fernandes To: paulmck@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, "# 5 . 5 . x" Subject: Re: [PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() Message-ID: <20200313035201.GB190951@google.com> References: <20200313024007.GA27492@paulmck-ThinkPad-P72> <20200313024046.27622-1-paulmck@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200313024046.27622-1-paulmck@kernel.org> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 12, 2020 at 07:40:45PM -0700, paulmck@kernel.org wrote: > From: "Paul E. McKenney" > > 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. I think Peter's new lockdep changes for NMI would also catch this issue. > > Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering") Reviewed-by: Joel Fernandes (Google) thanks, - Joel > Reported-by: Thomas Gleixner > Signed-off-by: Paul E. McKenney > Cc: # 5.5.x > --- > kernel/rcu/tree.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index d3f52c3..f7d3e48 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -825,7 +825,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq) > rcu_cleanup_after_idle(); > > incby = 1; > - } else if (tick_nohz_full_cpu(rdp->cpu) && > + } else if (irq && tick_nohz_full_cpu(rdp->cpu) && > rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE && > READ_ONCE(rdp->rcu_urgent_qs) && > !READ_ONCE(rdp->rcu_forced_tick)) { > -- > 2.9.5 >