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 E4FE7C4332F for ; Wed, 21 Dec 2022 19:24:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230264AbiLUTX7 (ORCPT ); Wed, 21 Dec 2022 14:23:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231834AbiLUTX4 (ORCPT ); Wed, 21 Dec 2022 14:23:56 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F637252B7 for ; Wed, 21 Dec 2022 11:23:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671650588; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=g0DCyUyGJiNNDAi1EtXEtA/eLbPEE2zu+zRGexCyTPU=; b=HOxFfQkotrNjVADX+nHK8du8LwFMcVtFRAWRqZdq7ytylxD8KTtj9xS7s/anFb6+kQOOKO 1Sl27HdN5+gZHw9E0ias5XsRtJ8/hdjLmWBGrlByEuXhnrnBsnAGNM9UCr8aIRaFE/I0Q1 3bwqFSMEb15H0oVxLNj7yv/PD91hIak= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-17-orX2Ra2pMDG_QBOez2Stwg-1; Wed, 21 Dec 2022 14:22:57 -0500 X-MC-Unique: orX2Ra2pMDG_QBOez2Stwg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0CEE9100F907; Wed, 21 Dec 2022 19:22:57 +0000 (UTC) Received: from [10.22.33.5] (unknown [10.22.33.5]) by smtp.corp.redhat.com (Postfix) with ESMTP id 749B9C16027; Wed, 21 Dec 2022 19:22:56 +0000 (UTC) Message-ID: <4d9559ca-9884-1942-907e-7edfff9be81a@redhat.com> Date: Wed, 21 Dec 2022 14:22:56 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH-tip v3] sched: Use kfree_rcu() in do_set_cpus_allowed() Content-Language: en-US To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira Cc: Phil Auld , linux-kernel@vger.kernel.org References: <20221205163936.2149640-1-longman@redhat.com> From: Waiman Long In-Reply-To: <20221205163936.2149640-1-longman@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/5/22 11:39, Waiman Long wrote: > Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in > do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously > set. Unfortunately, some of the callers of do_set_cpus_allowed() > may have pi_lock held when calling it. So the following splats may be > printed especially when running with a PREEMPT_RT kernel: > > WARNING: possible circular locking dependency detected > BUG: sleeping function called from invalid context > > To avoid these problems, kfree_rcu() is used instead. An internal > cpumask_rcuhead union is created for the sole purpose of facilitating > the use of kfree_rcu() to free the cpumask. > > Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") > Suggested-by: Peter Zijlstra > Signed-off-by: Waiman Long > --- > kernel/sched/core.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > > [v3: Fix build problem reported by kernel test robot] > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 57e5932f81a9..155b6cfe119a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2604,9 +2604,19 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) > .user_mask = NULL, > .flags = SCA_USER, /* clear the user requested mask */ > }; > + union cpumask_rcuhead { > + cpumask_t cpumask; > + struct rcu_head rcu; > + }; > > __do_set_cpus_allowed(p, &ac); > - kfree(ac.user_mask); > + > + /* > + * Because this is called with p->pi_lock held, it is not possible > + * to use kfree() here (when PREEMPT_RT=y), therefore punt to using > + * kfree_rcu(). > + */ > + kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu); > } > > int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, > @@ -8220,7 +8230,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) > struct affinity_context ac; > struct cpumask *user_mask; > struct task_struct *p; > - int retval; > + int retval, size; > > rcu_read_lock(); > > @@ -8253,7 +8263,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) > if (retval) > goto out_put_task; > > - user_mask = kmalloc(cpumask_size(), GFP_KERNEL); > + /* > + * See do_set_cpus_allowed() for the rcu_head usage. > + */ > + size = max_t(int, cpumask_size(), sizeof(struct rcu_head)); > + user_mask = kmalloc(size, GFP_KERNEL); > if (!user_mask) { > retval = -ENOMEM; > goto out_put_task; Hi Peter, Is this patch good enough to be merged as commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") is now in the Linus' tree? Thanks, Longman