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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 E8384C433E7 for ; Mon, 31 Aug 2020 18:03:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B34402083E for ; Mon, 31 Aug 2020 18:03:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598897000; bh=Zv8CPkwO+8Sx8yjhF3kXqyIGO3+PF6wlIFtXzoJQavw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=sPzXREIObypyjQQKi6jd26QYxcOCqQFuQt+uwqcLyvd0iSv6YFLomg6OJsWBpd3hS dUU5K9Zyy6ZT/9lQuRaaHBGFQJnpARBD6Fk46htK+UQ4gphf73tk2/qOrqh+7rdaeN p08WCoB/y0FFB/pfvMXnyEv4PXsUKf8weWl73QXs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729252AbgHaSDS (ORCPT ); Mon, 31 Aug 2020 14:03:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:35776 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728756AbgHaSBY (ORCPT ); Mon, 31 Aug 2020 14:01:24 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (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 9086920866; Mon, 31 Aug 2020 18:01:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598896883; bh=Zv8CPkwO+8Sx8yjhF3kXqyIGO3+PF6wlIFtXzoJQavw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nUkdiMtGmBH5rc5Mis/B3HC1DZ2jg4moYq59lTM1pi+jCF+8uF53hFRAEG0kaEh6U vtWWFAzdNfoxNgjfoSt7B/8jQnL6HsNQif2qJLMiZlkrKemgRzBicK1fmat3BXhckM K1x04Wc8X+PZ7kkmFkzK4mCE26xSlkTn0Z61//MA= 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" Subject: [PATCH tip/core/rcu 12/24] rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_resched_ns Date: Mon, 31 Aug 2020 11:01:04 -0700 Message-Id: <20200831180116.32690-12-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200831180050.GA32590@paulmck-ThinkPad-P72> References: <20200831180050.GA32590@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" Given that sysfs can change the value of rcu_resched_ns at any time, this commit adds a READ_ONCE() to the sole access to that variable. While in the area, this commit also adds bounds checking, clamping the value to at least a millisecond, but no longer than a second. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 1dca14c..da05afc 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2394,8 +2394,12 @@ static void rcu_do_batch(struct rcu_data *rdp) div = READ_ONCE(rcu_divisor); div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div; bl = max(rdp->blimit, pending >> div); - if (unlikely(bl > 100)) - tlimit = local_clock() + rcu_resched_ns; + if (unlikely(bl > 100)) { + long rrn = READ_ONCE(rcu_resched_ns); + + rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn; + tlimit = local_clock() + rrn; + } trace_rcu_batch_start(rcu_state.name, rcu_segcblist_n_cbs(&rdp->cblist), bl); rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl); -- 2.9.5