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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE38BC433EF for ; Thu, 2 Dec 2021 00:29:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354278AbhLBAcl (ORCPT ); Wed, 1 Dec 2021 19:32:41 -0500 Received: from sin.source.kernel.org ([145.40.73.55]:51878 "EHLO sin.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344661AbhLBAcj (ORCPT ); Wed, 1 Dec 2021 19:32:39 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 45772CE213A; Thu, 2 Dec 2021 00:29:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8FB48C53FAD; Thu, 2 Dec 2021 00:29:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638404954; bh=2v7+FPf9diZj5Aa7QlJClMx/gzTSbjL4TQgGFYiUYIE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=X0qb98MchxgKJIryzrF7a80+eIvdU39ApB+WyLPiI6RhwOVBXtPXnXctYaxil838w 2k4UlgWBkUpc+S96r1hU0hYXdT9hnU7iHNYMui2AoGIq7B293/2aMlU1pvSAZBX6eu PuL09w+XK4zhbbaBvtz9zMvz/9hEJy85uQUnFV+0tdYgSL9Tipmm2/ma3YIfYKLyyO dLTfi9aSFSg74V8BU4Ag4Sa4ZVb69fFjPFYVXcaB8fhPJff1Dicpa9fNde8+z5C/VP 8FJxmXyHVZOt3/QiePTDChCgBpjxdJz7L9iJx2arf1Ot5ohAGSIT7qmzyeNGiKJfTW RATmUF2IRKS2Q== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 5FD2C5C1108; Wed, 1 Dec 2021 16:29:14 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.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, Frederic Weisbecker , Valentin Schneider , Sebastian Andrzej Siewior , Boqun Feng , Neeraj Upadhyay , Uladzislau Rezki , "Paul E . McKenney" Subject: [PATCH rcu 02/18] rcu/nocb: Make local rcu_nocb_lock_irqsave() safe against concurrent deoffloading Date: Wed, 1 Dec 2021 16:28:56 -0800 Message-Id: <20211202002912.3127710-2-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20211202002848.GA3127439@paulmck-ThinkPad-P17-Gen-1> References: <20211202002848.GA3127439@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: Frederic Weisbecker rcu_nocb_lock_irqsave() can be preempted between the call to rcu_segcblist_is_offloaded() and the actual locking. This matters now that rcu_core() is preemptible on PREEMPT_RT and the (de-)offloading process can interrupt the softirq or the rcuc kthread. As a result we may locklessly call into code that requires nocb locking. In practice this is a problem while we accelerate callbacks on rcu_core(). Simply disabling interrupts before (instead of after) checking the NOCB offload state fixes the issue. Reported-and-tested-by: Valentin Schneider Tested-by: Sebastian Andrzej Siewior Signed-off-by: Frederic Weisbecker Cc: Valentin Schneider Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: Josh Triplett Cc: Joel Fernandes Cc: Boqun Feng Cc: Neeraj Upadhyay Cc: Uladzislau Rezki Cc: Thomas Gleixner Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.h | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 305cf6aeb4086..4f6c67b3ccd5e 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -447,12 +447,16 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp); #ifdef CONFIG_RCU_NOCB_CPU static void __init rcu_organize_nocb_kthreads(void); -#define rcu_nocb_lock_irqsave(rdp, flags) \ -do { \ - if (!rcu_segcblist_is_offloaded(&(rdp)->cblist)) \ - local_irq_save(flags); \ - else \ - raw_spin_lock_irqsave(&(rdp)->nocb_lock, (flags)); \ + +/* + * Disable IRQs before checking offloaded state so that local + * locking is safe against concurrent de-offloading. + */ +#define rcu_nocb_lock_irqsave(rdp, flags) \ +do { \ + local_irq_save(flags); \ + if (rcu_segcblist_is_offloaded(&(rdp)->cblist)) \ + raw_spin_lock(&(rdp)->nocb_lock); \ } while (0) #else /* #ifdef CONFIG_RCU_NOCB_CPU */ #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags) -- 2.31.1.189.g2e36527f23