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 056DBC4332F for ; Thu, 22 Dec 2022 20:19:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230289AbiLVUTX (ORCPT ); Thu, 22 Dec 2022 15:19:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47046 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229704AbiLVUTV (ORCPT ); Thu, 22 Dec 2022 15:19:21 -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 AE99112A88 for ; Thu, 22 Dec 2022 12:18:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671740316; 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=qkgT/rx+rJzPLcB9hasQHzxYWnSSI0xemioCpjMf6Jg=; b=TkjYmXtHZ/M7QFtAJY9JdjgLVzPihMQTBrux1yvdWNS/4dVhDtCPNIubvsrhlMy1PuCZUF BIHZcma7/4codlQt+8+hLc0z1JUfnSLmy8DQD39Xs640rd6v0T5k27wefVEl4AF0UW+JZO 2neLQITLRMdD0Bu5L1gVSq4Lg0OHAPM= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-471-orCGrTcfP6S2CxRVfCvOWA-1; Thu, 22 Dec 2022 15:18:30 -0500 X-MC-Unique: orCGrTcfP6S2CxRVfCvOWA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 116D71C0CE6B; Thu, 22 Dec 2022 20:18:30 +0000 (UTC) Received: from [10.22.33.48] (unknown [10.22.33.48]) by smtp.corp.redhat.com (Postfix) with ESMTP id 82D2D112132C; Thu, 22 Dec 2022 20:18:29 +0000 (UTC) Message-ID: <56792f82-951e-04c5-f7ea-fbf9ab375eec@redhat.com> Date: Thu, 22 Dec 2022 15:18:29 -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: Peter Zijlstra Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Phil Auld , linux-kernel@vger.kernel.org References: <20221205163936.2149640-1-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/22/22 14:32, Peter Zijlstra wrote: > On Mon, Dec 05, 2022 at 11:39:36AM -0500, 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; > AFAICT you forgot dup_user_cpus_ptr(). I haven't received any response from you for a while. So it is just a ping. Of course, I am aware that there is another dup_user_cpus_ptr() patch ouststanding. I will of course talk about that when you respond. I also have a pending rwsem patch series waiting for your review:-) Cheers, Longman