From mboxrd@z Thu Jan 1 00:00:00 1970 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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 4B796C43387 for ; Fri, 18 Jan 2019 12:28:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 251FF2087E for ; Fri, 18 Jan 2019 12:28:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727716AbfARM15 (ORCPT ); Fri, 18 Jan 2019 07:27:57 -0500 Received: from mga05.intel.com ([192.55.52.43]:2175 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727655AbfARM1y (ORCPT ); Fri, 18 Jan 2019 07:27:54 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Jan 2019 04:27:53 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,491,1539673200"; d="scan'208";a="268136115" Received: from elena-thinkpad-x230.fi.intel.com ([10.237.68.34]) by orsmga004.jf.intel.com with ESMTP; 18 Jan 2019 04:27:50 -0800 From: Elena Reshetova To: mingo@redhat.com Cc: peterz@infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, keescook@chromium.org, tglx@linutronix.de, Elena Reshetova Subject: [PATCH 3/5] sched: convert numa_group.refcount to refcount_t Date: Fri, 18 Jan 2019 14:27:28 +0200 Message-Id: <1547814450-18902-4-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1547814450-18902-1-git-send-email-elena.reshetova@intel.com> References: <1547814450-18902-1-git-send-email-elena.reshetova@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable numa_group.refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. **Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. The full comparison can be seen in https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon in state to be merged to the documentation tree. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the numa_group.refcount it might make a difference in following places: - get_numa_group(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_numa_group(): decrement in refcount_dec_and_test() only provides RELEASE ordering and control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Signed-off-by: Elena Reshetova --- kernel/sched/fair.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7303e0b..32a2382 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1035,7 +1035,7 @@ unsigned int sysctl_numa_balancing_scan_size = 256; unsigned int sysctl_numa_balancing_scan_delay = 1000; struct numa_group { - atomic_t refcount; + refcount_t refcount; spinlock_t lock; /* nr_tasks, tasks */ int nr_tasks; @@ -1104,7 +1104,7 @@ static unsigned int task_scan_start(struct task_struct *p) unsigned long shared = group_faults_shared(ng); unsigned long private = group_faults_priv(ng); - period *= atomic_read(&ng->refcount); + period *= refcount_read(&ng->refcount); period *= shared + 1; period /= private + shared + 1; } @@ -1127,7 +1127,7 @@ static unsigned int task_scan_max(struct task_struct *p) unsigned long private = group_faults_priv(ng); unsigned long period = smax; - period *= atomic_read(&ng->refcount); + period *= refcount_read(&ng->refcount); period *= shared + 1; period /= private + shared + 1; @@ -2203,12 +2203,12 @@ static void task_numa_placement(struct task_struct *p) static inline int get_numa_group(struct numa_group *grp) { - return atomic_inc_not_zero(&grp->refcount); + return refcount_inc_not_zero(&grp->refcount); } static inline void put_numa_group(struct numa_group *grp) { - if (atomic_dec_and_test(&grp->refcount)) + if (refcount_dec_and_test(&grp->refcount)) kfree_rcu(grp, rcu); } @@ -2229,7 +2229,7 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags, if (!grp) return; - atomic_set(&grp->refcount, 1); + refcount_set(&grp->refcount, 1); grp->active_nodes = 1; grp->max_faults_cpu = 0; spin_lock_init(&grp->lock); -- 2.7.4