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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D4B8C433F5 for ; Tue, 19 Oct 2021 00:08:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BB2C6128B for ; Tue, 19 Oct 2021 00:08:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234109AbhJSAK4 (ORCPT ); Mon, 18 Oct 2021 20:10:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:50402 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233969AbhJSAKq (ORCPT ); Mon, 18 Oct 2021 20:10:46 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id DFFC26134F; Tue, 19 Oct 2021 00:08:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634602114; bh=SUELVCRP5ACiu9FTbVAeY3f2v6/npNMQ+AvNWYclvy0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y9nabvqHJCbOOvcWWrbmqGAMPK1KQ4wfw13n17Xm5auxYE7BKQsQjE0i/vqgLK85i rP7e3DdVxBjUUxpis/R91J8/9kFyr3yzqfrhIVSAy30/NXIxSICSYI/vgCANgzWr1F 48sDhquNSBij+izw36MRedHoEbk0csT/L07HaJTF40fDutNovFw5TrOgKgGxkB0AQj ze2PQqQ2hIvkXV0RlRzyjI+CvHWrc/A0zD3Z/HV8xsGM7dJwk7Q94RgF0Mq1A3taDh BP4PKYhRrqsFRvNsj0MrlMj9MhT/6MRxiFbNKCEB+gZwL0HRnA98rR4oBxLw7fj0os 1S/SCI0Rigz4w== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Sebastian Andrzej Siewior , Valentin Schneider , Peter Zijlstra , Uladzislau Rezki , Thomas Gleixner , Valentin Schneider , Boqun Feng , Neeraj Upadhyay , Josh Triplett , Joel Fernandes Subject: [PATCH 04/10] rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe Date: Tue, 19 Oct 2021 02:08:10 +0200 Message-Id: <20211019000816.455375-5-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211019000816.455375-1-frederic@kernel.org> References: <20211019000816.455375-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When callbacks are offloaded, the NOCB kthreads handle the callbacks progression on behalf of rcu_core(). However during the (de-)offloading process, the kthread may not be entirely up to the task. As a result some callbacks grace period sequence number may remain stale for a while because rcu_core() won't take care of them either. Fix this with forcing callbacks acceleration from rcu_core() as long as the offloading process isn't complete. 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.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 4869a6856bf1..a43924244000 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2288,6 +2288,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp) unsigned long flags; unsigned long mask; bool needwake = false; + bool needacc = false; struct rcu_node *rnp; WARN_ON_ONCE(rdp->cpu != smp_processor_id()); @@ -2315,16 +2316,29 @@ rcu_report_qs_rdp(struct rcu_data *rdp) * This GP can't end until cpu checks in, so all of our * callbacks can be processed during the next GP. * - * NOCB kthreads have their own way to deal with that. + * NOCB kthreads have their own way to deal with that... */ - if (!rcu_rdp_is_offloaded(rdp)) + if (!rcu_rdp_is_offloaded(rdp)) { needwake = rcu_accelerate_cbs(rnp, rdp); + } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) { + /* + * ...but NOCB kthreads may miss or delay callbacks acceleration + * if in the middle of a (de-)offloading process. + */ + needacc = true; + } rcu_disable_urgency_upon_qs(rdp); rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); /* ^^^ Released rnp->lock */ if (needwake) rcu_gp_kthread_wake(); + + if (needacc) { + rcu_nocb_lock_irqsave(rdp, flags); + rcu_accelerate_cbs_unlocked(rnp, rdp); + rcu_nocb_unlock_irqrestore(rdp, flags); + } } } -- 2.25.1