From nobody Fri Sep 19 10:27:41 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 12BA6C43217 for ; Fri, 25 Nov 2022 02:41:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229731AbiKYClB (ORCPT ); Thu, 24 Nov 2022 21:41:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47334 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229695AbiKYCky (ORCPT ); Thu, 24 Nov 2022 21:40:54 -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 16A212613B for ; Thu, 24 Nov 2022 18:39:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669343995; 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=2xUQo86tA4szHqQI1SxOm+Ty0sm2LlLndvkk5Nb5uus=; b=MLXC08I67mYJnFpTPjyOi9+h3LS74fcSi2XZQZbYHcL17YTfkOi0ZbFAc5HGhhwm9lMnbw 7uryNIpmDFLqLy+skmxvINojWBTTE8UPL23wRIRl8WSh4TyvJXc0acmkpzmhyOa3jC0ymU fEcdxHyv6LguvJ/Aq+c4MIeMsV+B9FE= 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-208-18ukYN-PM3Cnv4bZ7F7TMw-1; Thu, 24 Nov 2022 21:39:51 -0500 X-MC-Unique: 18ukYN-PM3Cnv4bZ7F7TMw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 362111C068CF; Fri, 25 Nov 2022 02:39:51 +0000 (UTC) Received: from llong.com (unknown [10.22.32.81]) by smtp.corp.redhat.com (Postfix) with ESMTP id 79FF14B3FCE; Fri, 25 Nov 2022 02:39:50 +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 , Wenjie Li , =?UTF-8?q?David=20Wang=20=E7=8E=8B=E6=A0=87?= , linux-kernel@vger.kernel.org, Waiman Long Subject: [PATCH-tip v4] sched: Fix NULL user_cpus_ptr check in dup_user_cpus_ptr() Date: Thu, 24 Nov 2022 21:39:43 -0500 Message-Id: <20221125023943.1118603-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" In general, a non-null user_cpus_ptr will remain set until the task dies. A possible exception to this is the fact that do_set_cpus_allowed() will clear a non-null user_cpus_ptr. To allow this possible racing condition, we need to check for NULL user_cpus_ptr under the pi_lock before duping the user mask. Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allo= wed()") Signed-off-by: Waiman Long --- kernel/sched/core.c | 32 ++++++++++++++++++++++++++++---- 1 file changed, 28 insertions(+), 4 deletions(-) [v4] Minor comment update diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8df51b08bb38..f2b75faaf71a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2624,19 +2624,43 @@ void do_set_cpus_allowed(struct task_struct *p, con= st struct cpumask *new_mask) int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node) { + cpumask_t *user_mask; unsigned long flags; =20 + /* + * Always clear dst->user_cpus_ptr first as their user_cpus_ptr's + * may differ by now due to racing. + */ + dst->user_cpus_ptr =3D NULL; + + /* + * This check is racy and losing the race is a valid situation. + * It is not worth the extra overhead of taking the pi_lock on + * every fork/clone. + */ if (!src->user_cpus_ptr) return 0; =20 - dst->user_cpus_ptr =3D kmalloc_node(cpumask_size(), GFP_KERNEL, node); - if (!dst->user_cpus_ptr) + user_mask =3D kmalloc_node(cpumask_size(), GFP_KERNEL, node); + if (!user_mask) return -ENOMEM; =20 - /* Use pi_lock to protect content of user_cpus_ptr */ + /* + * Use pi_lock to protect content of user_cpus_ptr + * + * Though unlikely, user_cpus_ptr can be reset to NULL by a concurrent + * do_set_cpus_allowed(). + */ raw_spin_lock_irqsave(&src->pi_lock, flags); - cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr); + if (src->user_cpus_ptr) { + swap(dst->user_cpus_ptr, user_mask); + cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr); + } raw_spin_unlock_irqrestore(&src->pi_lock, flags); + + if (unlikely(user_mask)) + kfree(user_mask); + return 0; } =20 --=20 2.31.1