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 DA349C433F5 for ; Wed, 29 Sep 2021 22:11:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C4D3660FC2 for ; Wed, 29 Sep 2021 22:11:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347315AbhI2WMt (ORCPT ); Wed, 29 Sep 2021 18:12:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:33014 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347235AbhI2WMb (ORCPT ); Wed, 29 Sep 2021 18:12:31 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5815C61529; Wed, 29 Sep 2021 22:10:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1632953449; bh=5PvqZQ5qnk2I6xO0f6MuVKzqATnTaiknkLZJeVgkG6E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KR6ul31Lk8Y61P7V2V7Y2OwcjrXy0kYrFZW/c6h68bUrYBEXOE48gqmw9xZqqXhu/ R/VKaw4QH+gLdqt7OU03RRYdH4lo4zvzEBm2QOSATZoxbiYlfottyLGGcgDhoRhBTw DOJh4MtvEieXcfiZ0SCvdb9KZ5OOhJnitThSNDzDFBD6R3Mj2fdQ6JbnBisHjTudMU saSpKioKqMs+Y0SJLYRnn9TrEE7dr04GejzzLOGgc7XAE/LhKR77azrYmA8kMRK2q8 yXHImdmbF7nVq+la/wIYyzUWKfXGAAUTcHBdyRSdoqMFV9g+G3Jx5hTCplgwY9kd1i Gg+vleksO25xQ== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Sebastian Andrzej Siewior , Peter Zijlstra , Uladzislau Rezki , Valentin Schneider , Thomas Gleixner , Boqun Feng , Neeraj Upadhyay , Josh Triplett , Joel Fernandes , rcu@vger.kernel.org Subject: [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Date: Thu, 30 Sep 2021 00:10:12 +0200 Message-Id: <20210929221012.228270-12-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210929221012.228270-1-frederic@kernel.org> References: <20210929221012.228270-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 that 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 Fix that with moving the rcu_core() self-invocation to rcu_core() itself, irrespective of the rdp offloaded state. 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 --- 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 b538094e21d9..600bffe4f121 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2470,7 +2470,6 @@ 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; @@ -2592,9 +2591,6 @@ 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); } @@ -2781,8 +2777,12 @@ 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); -- 2.25.1