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 17C4AC433EF for ; Thu, 2 Dec 2021 00:29:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354420AbhLBAc7 (ORCPT ); Wed, 1 Dec 2021 19:32:59 -0500 Received: from sin.source.kernel.org ([145.40.73.55]:51962 "EHLO sin.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345031AbhLBAcl (ORCPT ); Wed, 1 Dec 2021 19:32:41 -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 00639CE213B; Thu, 2 Dec 2021 00:29:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10C3CC58332; Thu, 2 Dec 2021 00:29:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638404955; bh=GHgGsDCq17POu9DvYzdzZrkC23Mrj2IPIVzBqt/uUnE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=p27+L0n0+0Su0ARbygCsvpjseu9Gr8Ko+ylfJEr5ZAZDc+A11iUq+j6Im2HV9Gzep KecqD6595+/NvwNC4ribBr75BobF+GttIU2ih57gc+GOzHYUdwBHD/x1djDojb/zUq a41TeW/A1G1ZTqMP1v3M9SI7pplZQVNiI4pHAsO+IuxtSlkyAUFziIOqkmGpj59RW/ PcpgihlpDVlC2WUJEe8ekmv0FdgQ2aygKtNobBdXVKjtNAqVtInQg5nElaaMagOhDW VlUxOj6z9QKszpnSPnfN3v/LwfX8fx6FR6whiLfLPiZbDy6UqM6cuJNwWFDgfwh1CR oG9Bn1aEaScPA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 7468A5C1411; 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 12/18] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Date: Wed, 1 Dec 2021 16:29:06 -0800 Message-Id: <20211202002912.3127710-12-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_core() tries to ensure that its self-invocation in case of callbacks overload only happen in softirq/rcuc mode. Indeed it doesn't make sense to trigger local RCU core from nocb_cb kthread since it can execute on a CPU different from the target rdp. Also in case of overload, the nocb_cb kthread simply iterates a new loop of callbacks processing. However the "offloaded" check that aims at preventing misplaced rcu_core() invocations is wrong. First of all that state is volatile and second: softirq/rcuc can execute while the target rdp is offloaded. As a result rcu_core() can be invoked on the wrong CPU while in the process of (de-)offloading. Fix that with moving the rcu_core() self-invocation to rcu_core() itself, irrespective of the rdp offloaded state. 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 | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 1b31fad9f1a0a..03c038f324a09 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2460,7 +2460,6 @@ static void rcu_do_batch(struct rcu_data *rdp) int div; bool __maybe_unused empty; unsigned long flags; - const bool offloaded = rcu_rdp_is_offloaded(rdp); struct rcu_head *rhp; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); long bl, count = 0; @@ -2582,9 +2581,6 @@ static void rcu_do_batch(struct rcu_data *rdp) rcu_nocb_unlock_irqrestore(rdp, flags); - /* Re-invoke RCU core processing if there are callbacks remaining. */ - if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist)) - invoke_rcu_core(); tick_dep_clear_task(current, TICK_DEP_BIT_RCU); } @@ -2771,8 +2767,12 @@ static __latent_entropy void rcu_core(void) /* If there are callbacks ready, invoke them. */ if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) && - likely(READ_ONCE(rcu_scheduler_fully_active))) + likely(READ_ONCE(rcu_scheduler_fully_active))) { rcu_do_batch(rdp); + /* Re-invoke RCU core processing if there are callbacks remaining. */ + if (rcu_segcblist_ready_cbs(&rdp->cblist)) + invoke_rcu_core(); + } /* Do any needed deferred wakeups of rcuo kthreads. */ do_nocb_deferred_wakeup(rdp); -- 2.31.1.189.g2e36527f23