From nobody Mon Apr 6 09:48:19 2026 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 B550EC6FA89 for ; Thu, 8 Sep 2022 19:42:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231467AbiIHTmX (ORCPT ); Thu, 8 Sep 2022 15:42:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229889AbiIHTmD (ORCPT ); Thu, 8 Sep 2022 15:42:03 -0400 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 6B994D51D4 for ; Thu, 8 Sep 2022 12:42:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1662666119; 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=ygU5n+vDab/JrahhgIYA9NLv/bE0KEdNWKARdUa/DEs=; b=BgimrHCsiMZw+VHpdeY1feMqqhPwLZ2e6m717qMNsLjzPh0gOi2tajLFNvviCDLWHo3R0O UTxoftsJ/i9Nf1l5ClWlWftU/BVtrwQA3I1V2vmKDqYLuWW7/2HugwhabsiRygL2WJ+JaV bWmxi9FGgxHJbrd+BXWiDLSWscu/gdA= 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-615-n77__nT_NPm4okGGTNKDEg-1; Thu, 08 Sep 2022 15:41:55 -0400 X-MC-Unique: n77__nT_NPm4okGGTNKDEg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4EAE2101A56C; Thu, 8 Sep 2022 19:41:54 +0000 (UTC) Received: from llong.com (unknown [10.22.9.66]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9FE7D1415117; Thu, 8 Sep 2022 19:41:53 +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 , Valentin Schneider , Tejun Heo , Zefan Li , Johannes Weiner , Will Deacon Cc: linux-kernel@vger.kernel.org, Linus Torvalds , Lai Jiangshan , Waiman Long Subject: [PATCH v8 5/7] sched: Handle set_cpus_allowed_ptr() & sched_setaffinity() race Date: Thu, 8 Sep 2022 15:41:19 -0400 Message-Id: <20220908194121.858462-6-longman@redhat.com> In-Reply-To: <20220908194121.858462-1-longman@redhat.com> References: <20220908194121.858462-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.85 on 10.11.54.7 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Racing is possible between set_cpus_allowed_ptr() and sched_setaffinity() or between multiple sched_setaffinity() calls from different CPUs. To resolve these race conditions, we need to update both user_cpus_ptr and cpus_mask in a single lock critical section instead of separated ones. This requires moving the user_cpus_ptr update to set_cpus_allowed_common() by putting the user_mask into the affinity_context structure. This patch also changes the handling of the race between the sched_setaffinity() call and the changing of cpumask of the current cpuset. In case the new mask conflicts with newly updated cpuset, the cpus_mask will be reset to the cpuset cpumask and an error value of -EINVAL will be returned. If a previous user_cpus_ptr value exists, it will be swapped back in and the new_mask will be further restricted to what is allowed in the cpumask pointed to by the old user_cpus_ptr. Signed-off-by: Waiman Long --- kernel/sched/core.c | 44 +++++++++++++++++++++++++++----------------- kernel/sched/sched.h | 1 + 2 files changed, 28 insertions(+), 17 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b43b851c0399..1ba5d82d4f3c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2546,6 +2546,12 @@ void set_cpus_allowed_common(struct task_struct *p, = struct affinity_context *ctx =20 cpumask_copy(&p->cpus_mask, ctx->new_mask); p->nr_cpus_allowed =3D cpumask_weight(ctx->new_mask); + + /* + * Swap in a new user_cpus_ptr if SCA_USER flag set + */ + if (ctx->flags & SCA_USER) + swap(p->user_cpus_ptr, ctx->user_mask); } =20 static void @@ -8100,7 +8106,7 @@ __sched_setaffinity(struct task_struct *p, struct aff= inity_context *ctx) retval =3D dl_task_check_affinity(p, new_mask); if (retval) goto out_free_new_mask; -again: + retval =3D __set_cpus_allowed_ptr(p, ctx); if (retval) goto out_free_new_mask; @@ -8112,7 +8118,24 @@ __sched_setaffinity(struct task_struct *p, struct af= finity_context *ctx) * Just reset the cpumask to the cpuset's cpus_allowed. */ cpumask_copy(new_mask, cpus_allowed); - goto again; + + /* + * If SCA_USER is set, a 2nd call to __set_cpus_allowed_ptr() + * will restore the previous user_cpus_ptr value. + * + * In the unlikely event a previous user_cpus_ptr exists, + * we need to further restrict the mask to what is allowed + * by that old user_cpus_ptr. + */ + if (unlikely((ctx->flags & SCA_USER) && ctx->user_mask)) { + bool empty =3D !cpumask_and(new_mask, new_mask, + ctx->user_mask); + + if (WARN_ON_ONCE(empty)) + cpumask_copy(new_mask, cpus_allowed); + } + __set_cpus_allowed_ptr(p, ctx); + retval =3D -EINVAL; } =20 out_free_new_mask: @@ -8168,25 +8191,12 @@ long sched_setaffinity(pid_t pid, const struct cpum= ask *in_mask) cpumask_copy(user_mask, in_mask); ac =3D (struct affinity_context){ .new_mask =3D in_mask, + .user_mask =3D user_mask, .flags =3D SCA_USER, }; =20 retval =3D __sched_setaffinity(p, &ac); - - /* - * Save in_mask into user_cpus_ptr after a successful - * __sched_setaffinity() call. pi_lock is used to synchronize - * changes to user_cpus_ptr. - */ - if (!retval) { - unsigned long flags; - - /* Use pi_lock to synchronize changes to user_cpus_ptr */ - raw_spin_lock_irqsave(&p->pi_lock, flags); - swap(p->user_cpus_ptr, user_mask); - raw_spin_unlock_irqrestore(&p->pi_lock, flags); - } - kfree(user_mask); + kfree(ac.user_mask); =20 out_put_task: put_task_struct(p); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 1927c02f68fa..110e13b7d78b 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2159,6 +2159,7 @@ extern const u32 sched_prio_to_wmult[40]; =20 struct affinity_context { const struct cpumask *new_mask; + struct cpumask *user_mask; unsigned int flags; }; =20 --=20 2.31.1