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 5C6C0C4167B for ; Tue, 31 Oct 2023 10:52:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343992AbjJaKwp (ORCPT ); Tue, 31 Oct 2023 06:52:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53330 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230370AbjJaKwo (ORCPT ); Tue, 31 Oct 2023 06:52:44 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 36BEDA1 for ; Tue, 31 Oct 2023 03:52:42 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1293DC433C7; Tue, 31 Oct 2023 10:52:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1698749561; bh=QxPlull2BB81b83iUvmVPFPs6Ac/bnfOsodU2R8tfYQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jAjmyDoctca301AH94jcqEQNYV94SCsDaMdhrat+N8Zp4heS2yTzo7ygvXSV5DzeD WRHnI7D/HVb00nv37CLilasjkWpEdsd4ROilAvuxmd328fkHD9I7oTEZe/0/bviMOc IComnX5UbWyJuk1KioYViUwelvoJfmxiSviNfWQRNoJSiVWYqHLlD7AkBUnpwEo19i /5LfbK4B6Pf2H28dd/JcX3YTl/4/5jY5WrNbpDk6/6ItIi/eY5Hy4rrwFz7uCzyZE2 Ag5X95On54Bd1HwSglV38gSqrMjPaps2M6IqeJHRRS3fr7GHwQueJXZoIAdVE9+hlW fmG44iAoysiTw== Date: Tue, 31 Oct 2023 11:52:38 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: Waiman Long , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , linux-kernel@vger.kernel.org, Phil Auld , kernel test robot , aubrey.li@linux.intel.com, yu.c.chen@intel.com, paulmck@kernel.org, quic_neeraju@quicinc.com, joel@joelfernandes.org, josh@joshtriplett.org, boqun.feng@gmail.com, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang1211@gmail.com Subject: Re: [PATCH] sched: Don't call any kfree*() API in do_set_cpus_allowed() Message-ID: References: <20231031001418.274187-1-longman@redhat.com> <20231031085308.GB35651@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231031085308.GB35651@noisy.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 31, 2023 at 09:53:08AM +0100, Peter Zijlstra wrote: > On Mon, Oct 30, 2023 at 08:14:18PM -0400, Waiman Long wrote: > > Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in > > do_set_cpus_allowed()") added a kfree() call to free any user > > provided affinity mask, if present. It was changed later to use > > kfree_rcu() in commit 9a5418bc48ba ("sched/core: Use kfree_rcu() > > in do_set_cpus_allowed()") to avoid a circular locking dependency > > problem. > > > > It turns out that even kfree_rcu() isn't safe for avoiding > > circular locking problem. As reported by kernel test robot, > > the following circular locking dependency still exists: > > > > &rdp->nocb_lock --> rcu_node_0 --> &rq->__lock > > > > So no kfree*() API can be used in do_set_cpus_allowed(). To prevent > > memory leakage, the unused user provided affinity mask is now saved in a > > lockless list to be reused later by subsequent sched_setaffinity() calls. > > > > Without kfree_rcu(), the internal cpumask_rcuhead union can be removed > > too as a lockless list entry only holds a single pointer. > > > > Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") > > Bah, or we fix RCU... Paul, how insane is the below? Makes sense. We can't remove &rdp->nocb_lock --> rcu_node_0 but we can (and should) indeed remove rcu_node_0 --> &rq->__lock Just a detail below: > @@ -2284,10 +2289,13 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) > } > for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) { > rdp = per_cpu_ptr(&rcu_data, cpu); > - if (f(rdp)) { > + ret = f(rdp); > + if (ret > 0) { > mask |= rdp->grpmask; > rcu_disable_urgency_upon_qs(rdp); > } > + if (ret < 0) > + rsmask |= 1UL << (cpu - rnp->grplo); I guess this can be simplified with rsmask |= rdp->grpmask; Thanks. > } > if (mask != 0) { > /* Idle/offline CPUs, report (releases rnp->lock). */ > @@ -2296,6 +2304,9 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) > /* Nothing to do here, so just drop the lock. */ > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > } > + > + for_each_leaf_node_cpu_mask(rnp, cpu, rsmask) > + resched_cpu(cpu); > } > } >