From nobody Thu Apr 16 00:40:35 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 5A8DBC433FE for ; Tue, 22 Nov 2022 19:08:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231766AbiKVTIP (ORCPT ); Tue, 22 Nov 2022 14:08:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35922 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234428AbiKVTIL (ORCPT ); Tue, 22 Nov 2022 14:08:11 -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 5243B88F8B for ; Tue, 22 Nov 2022 11:07:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669144035; 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=EdhjQKV+ZzYu+PMSguTcq06YsxJdSb6Km7Bwb+5zyus=; b=fw2579WgS8pqmua8csJ2z+dhBoXe2hsxJhX892kAOGfW8KSa3YoBSiB9ChPQO3wRVCAoxL vNQaZgCNLUERVUTLTj2OMBom7VdSUSr2ErzbpLSY8oUsYeExDH2wuqMJWvugU5P8So6GqE +R9AJqwRTpJVD0L90DO/slr+G/3BdRM= 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-397-y6aAC1uTNdCLD6k0LmOdjw-1; Tue, 22 Nov 2022 14:07:11 -0500 X-MC-Unique: y6aAC1uTNdCLD6k0LmOdjw-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 941F83826A44; Tue, 22 Nov 2022 19:07:10 +0000 (UTC) Received: from llong.com (unknown [10.22.17.223]) by smtp.corp.redhat.com (Postfix) with ESMTP id E82D11415102; Tue, 22 Nov 2022 19:07:09 +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] sched: Fix NULL user_cpus_ptr check in dup_user_cpus_ptr() Date: Tue, 22 Nov 2022 14:06:53 -0500 Message-Id: <20221122190653.818506-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 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 | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8df51b08bb38..f447a6285ea2 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2625,7 +2625,14 @@ int dup_user_cpus_ptr(struct task_struct *dst, struc= t task_struct *src, int node) { unsigned long flags; + cpumask_t *user_mask =3D NULL; =20 + /* + * If there is a concurrent sched_setaffinity(), we may miss the + * newly updated user_cpus_ptr. However, a non-NULL user_cpus_ptr + * is relatively unlikely and it is not worth the extra overhead + * of taking the pi_lock on every fork/clone. + */ if (!src->user_cpus_ptr) return 0; =20 @@ -2633,10 +2640,22 @@ int dup_user_cpus_ptr(struct task_struct *dst, stru= ct task_struct *src, if (!dst->user_cpus_ptr) 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) + cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr); + else + swap(dst->user_cpus_ptr, user_mask); raw_spin_unlock_irqrestore(&src->pi_lock, flags); + + if (unlikely(user_mask)) + kfree(user_mask); + return 0; } =20 --=20 2.31.1