From nobody Thu Sep 18 15:36:51 2025 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 CE0ACC4332F for ; Mon, 5 Dec 2022 16:43:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233125AbiLEQnG (ORCPT ); Mon, 5 Dec 2022 11:43:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233062AbiLEQml (ORCPT ); Mon, 5 Dec 2022 11:42:41 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D71CD20F4E for ; Mon, 5 Dec 2022 08:39:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1670258394; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=UwGVjXumPQzL40l8TfKHByp/JK2YeK0whUHeU5OwBrM=; b=YMbzHNhQUOH10LZM0rtrFAskiEcjYyLp8y7g1nPXGNk4OvzYQpQGOuw77j5RacZT0XuXQn KNCv/mFaPV9qUZ1XUbLNbVjeCB8W/jUpiSNqlKtSxw5GR8wszI/wLz0hYHwr2Pg1DlVN4M nH3zIwmA10CEi8mz+MTQav4iSzBnSpw= 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-264-DhehImJqOyeSNq2O_-dU1w-1; Mon, 05 Dec 2022 11:39:52 -0500 X-MC-Unique: DhehImJqOyeSNq2O_-dU1w-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 428381C08787; Mon, 5 Dec 2022 16:39:52 +0000 (UTC) Received: from llong.com (unknown [10.22.9.203]) by smtp.corp.redhat.com (Postfix) with ESMTP id AA72A492B07; Mon, 5 Dec 2022 16:39:51 +0000 (UTC) From: Waiman Long 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, Waiman Long Subject: [PATCH-tip v3] sched: Use kfree_rcu() in do_set_cpus_allowed() Date: Mon, 5 Dec 2022 11:39:36 -0500 Message-Id: <20221205163936.2149640-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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_allo= wed()") 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, cons= t struct cpumask *new_mask) .user_mask =3D NULL, .flags =3D SCA_USER, /* clear the user requested mask */ }; + union cpumask_rcuhead { + cpumask_t cpumask; + struct rcu_head rcu; + }; =20 __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=3Dy), therefore punt to using + * kfree_rcu(). + */ + kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu); } =20 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 cpumas= k *in_mask) struct affinity_context ac; struct cpumask *user_mask; struct task_struct *p; - int retval; + int retval, size; =20 rcu_read_lock(); =20 @@ -8253,7 +8263,11 @@ long sched_setaffinity(pid_t pid, const struct cpuma= sk *in_mask) if (retval) goto out_put_task; =20 - user_mask =3D kmalloc(cpumask_size(), GFP_KERNEL); + /* + * See do_set_cpus_allowed() for the rcu_head usage. + */ + size =3D max_t(int, cpumask_size(), sizeof(struct rcu_head)); + user_mask =3D kmalloc(size, GFP_KERNEL); if (!user_mask) { retval =3D -ENOMEM; goto out_put_task; --=20 2.31.1