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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 00819C2BB1D for ; Fri, 13 Mar 2020 02:40:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C32F220737 for ; Fri, 13 Mar 2020 02:40:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584067249; bh=/XdpGgEtuWJXlpQYE6PfA/melM7UXnrXGPeSAla6eYc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=nmjWLVXIz04IhbrxeTpw6le+8u/MQC1SJDjAmQRi0mf1CZHSCJNy6Y8hVqRGorprk /ZWl8QrUxtbDJX08T57YsSmR06iUcj92EGc7ZaHeZ5LddJgqHcqtTmaXHR7duq2fMy FDHOX91P2JgjHQGJXxtHLcXR+VWJdXyZ9tcfRgms= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726526AbgCMCkt (ORCPT ); Thu, 12 Mar 2020 22:40:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:57642 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726099AbgCMCks (ORCPT ); Thu, 12 Mar 2020 22:40:48 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BDC5E20736; Fri, 13 Mar 2020 02:40:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584067248; bh=/XdpGgEtuWJXlpQYE6PfA/melM7UXnrXGPeSAla6eYc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Wz1Sz8P3k5NeYdAKmsHoK4qeEWGixq0O1Jo7Rjs86p4j6D5JKF7SDB2bbV6usoQrP gC6E8CnvC+Oov1Yp3lRocjxaRFhvx6mW9nSyEHga74oXsZQWeC01wzyf/qnSF6QpjC NnKq7qQFkvuijY12886BEi1720hoI5+n3yO9q8bQ= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: 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, joel@joelfernandes.org, "Paul E. McKenney" , "# 5 . 5 . x" Subject: [PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() Date: Thu, 12 Mar 2020 19:40:45 -0700 Message-Id: <20200313024046.27622-1-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200313024007.GA27492@paulmck-ThinkPad-P72> References: <20200313024007.GA27492@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering") 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