From patchwork Fri Sep 3 08:02:02 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Patrick Schaaf X-Patchwork-Id: 507006 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 769D9C433F5 for ; Fri, 3 Sep 2021 08:04:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4BCE960EBA for ; Fri, 3 Sep 2021 08:04:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348115AbhICIEI (ORCPT ); Fri, 3 Sep 2021 04:04:08 -0400 Received: from mo1.intermailgate.com ([91.203.103.210]:35666 "EHLO mo1.intermailgate.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348097AbhICIDh (ORCPT ); Fri, 3 Sep 2021 04:03:37 -0400 Received: from localhost (localhost [127.0.0.1]) by mo1.intermailgate.com (Postfix) with ESMTP id 151A181129 for ; Fri, 3 Sep 2021 10:02:20 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=bof.de; s=20180522; t=1630656140; bh=7sxlm7nJbtlV7Nt4e6oXIOnl/RObgDVNSgWjfz5AQq0=; h=From:Date:Subject:To; b=vel3tP+rev6vV5yk4OQVIqiNTJU1hIkWx1F4btHI0YXJJY03nLOmskQDaq2o7Zoej 0qChWQWtjbGtDltCTYZLzDA/CGYRGfWoqJxQxeflPwD2L2Krr3lbnimbnDx/Xf5guB LMXz2pwNYn8Vapo3C2UtLegc9DzryfSOBi/897YM= Received: from mail-lj1-f182.google.com (unknown [162.158.183.104]) by mo1.intermailgate.com (Postfix) with ESMTPSA id 9D3948106F for ; Fri, 3 Sep 2021 10:02:19 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=bof.de; s=20180522; t=1630656139; bh=7sxlm7nJbtlV7Nt4e6oXIOnl/RObgDVNSgWjfz5AQq0=; h=From:Date:Subject:To; b=t21DfmiAq/wlRHuGx0Ai0CHI5SaKK6uPq4dYJFpOY0oj5KUMDp6vNI75Tkg1Pg3si AOZYL0Br9mGXiYY8GBFXmuTEdNN2sXv/pkmoHBcdqE7NqsE3TknVl845xc2m9WWzDT hSWtJi1oQiisg3KC9GenKUkfH2vc2j1K+7sSVk5g= Received: by mail-lj1-f182.google.com with SMTP id q21so8304929ljj.6 for ; Fri, 03 Sep 2021 01:02:19 -0700 (PDT) X-Gm-Message-State: AOAM53223mMEkt9NMriURjnBtqZncxkE0irV1t9f3ljRMRL71J7MByMp aHpx8yYwYsfQY5+5+cqudXjJ11lA3WlKqfihuQw= X-Google-Smtp-Source: ABdhPJxmSiLEOLN78tct60+IXIHEqkW9q4lhD1rEAEBMnZD54LXGpnlv/OVTj74bqSNe3yEwklLzyfzaTBxH5eZFc2Q= X-Received: by 2002:a2e:960c:: with SMTP id v12mr1926576ljh.300.1630656139111; Fri, 03 Sep 2021 01:02:19 -0700 (PDT) MIME-Version: 1.0 From: Patrick Schaaf Date: Fri, 3 Sep 2021 10:02:02 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: [PATCH] for 5.4 : kthread: Fix PF_KTHREAD vs to_kthread() race To: stable@vger.kernel.org, Peter Zijlstra , Borislav Petkov Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org After 3 days of successfully running 5.4.143 with this patch attached and no issues, on a production workload (host + vms) of a busy webserver and mysql database, I request queueing this for a future 5.4 stable, like the 5.10 one requested by Borislav; copying his mail text in the hope that this is best form. please queue for 5.4 stable See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info. --- Commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 upstream. The kthread_is_per_cpu() construct relies on only being called on PF_KTHREAD tasks (per the WARN in to_kthread). This gives rise to the following usage pattern: if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p)) However, as reported by syzcaller, this is broken. The scenario is: CPU0 CPU1 (running p) (p->flags & PF_KTHREAD) // true begin_new_exec() me->flags &= ~(PF_KTHREAD|...); kthread_is_per_cpu(p) to_kthread(p) WARN(!(p->flags & PF_KTHREAD) <-- *SPLAT* Introduce __to_kthread() that omits the WARN and is sure to check both values. Use this to remove the problematic pattern for kthread_is_per_cpu() and fix a number of other kthread_*() functions that have similar issues but are currently not used in ways that would expose the problem. Notably kthread_func() is only ever called on 'current', while kthread_probe_data() is only used for PF_WQ_WORKER, which implies the task is from kthread_create*(). Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU") Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Patrick Schaaf if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) { diff --git a/kernel/kthread.c b/kernel/kthread.c index b2bac5d929d2..22750a8af83e 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -76,6 +76,25 @@ static inline struct kthread *to_kthread(struct task_struct *k) return (__force void *)k->set_child_tid; } +/* + * Variant of to_kthread() that doesn't assume @p is a kthread. + * + * Per construction; when: + * + * (p->flags & PF_KTHREAD) && p->set_child_tid + * + * the task is both a kthread and struct kthread is persistent. However + * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and + * begin_new_exec()). + */ +static inline struct kthread *__to_kthread(struct task_struct *p) +{ + void *kthread = (__force void *)p->set_child_tid; + if (kthread && !(p->flags & PF_KTHREAD)) + kthread = NULL; + return kthread; +} + void free_kthread_struct(struct task_struct *k) { struct kthread *kthread; @@ -176,10 +195,11 @@ void *kthread_data(struct task_struct *task) */ void *kthread_probe_data(struct task_struct *task) { - struct kthread *kthread = to_kthread(task); + struct kthread *kthread = __to_kthread(task); void *data = NULL; - probe_kernel_read(&data, &kthread->data, sizeof(data)); + if (kthread) + probe_kernel_read(&data, &kthread->data, sizeof(data)); return data; } @@ -490,9 +510,9 @@ void kthread_set_per_cpu(struct task_struct *k, int cpu) set_bit(KTHREAD_IS_PER_CPU, &kthread->flags); } -bool kthread_is_per_cpu(struct task_struct *k) +bool kthread_is_per_cpu(struct task_struct *p) { - struct kthread *kthread = to_kthread(k); + struct kthread *kthread = __to_kthread(p); if (!kthread) return false; @@ -1272,11 +1292,9 @@ EXPORT_SYMBOL(kthread_destroy_worker); */ void kthread_associate_blkcg(struct cgroup_subsys_state *css) { - struct kthread *kthread; + struct kthread *kthread = __to_kthread(current); + - if (!(current->flags & PF_KTHREAD)) - return; - kthread = to_kthread(current); if (!kthread) return; @@ -1298,13 +1316,10 @@ EXPORT_SYMBOL(kthread_associate_blkcg); */ struct cgroup_subsys_state *kthread_blkcg(void) { - struct kthread *kthread; + struct kthread *kthread = __to_kthread(current); - if (current->flags & PF_KTHREAD) { - kthread = to_kthread(current); - if (kthread) - return kthread->blkcg_css; - } + if (kthread) + return kthread->blkcg_css; return NULL; } EXPORT_SYMBOL(kthread_blkcg); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 74cb20f32f72..87d9fad9d01d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7301,7 +7301,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) return 0; /* Disregard pcpu kthreads; they are where they need to be. */ - if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p)) + if (kthread_is_per_cpu(p)) return 0;