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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED 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 09FB2C4360C for ; Sat, 13 Mar 2021 05:08:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB3F764FF5 for ; Sat, 13 Mar 2021 05:08:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231907AbhCMFIO (ORCPT ); Sat, 13 Mar 2021 00:08:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:42102 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231938AbhCMFIE (ORCPT ); Sat, 13 Mar 2021 00:08:04 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1F9CD64E41; Sat, 13 Mar 2021 05:08:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1615612084; bh=Wi6CK4S8qvNeM9MEPQ16Q3IB5iWStis3UQzR38APEZ4=; h=Date:From:To:Subject:In-Reply-To:From; b=GO4xTX9nZPWszKYY/jdgqGY6VVU9eqUt4fB2ZuaoWU0a9B7+qz/90YFy5Hjm83vf+ sC978aGhRiU6JIrrDOwPJ9oHcocWh824Kg8TYIqOccZd8hpWR5CAqDQ3KJyuoBs9Nw to00u+a0Zg8MG4UEG4EsgFvhiitHY/Xq2zfPeJPs= Date: Fri, 12 Mar 2021 21:08:03 -0800 From: Andrew Morton To: akpm@linux-foundation.org, linmiaohe@huawei.com, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, torvalds@linux-foundation.org, willy@infradead.org Subject: [patch 18/29] include/linux/sched/mm.h: use rcu_dereference in in_vfork() Message-ID: <20210313050803.CFTW-ffYI%akpm@linux-foundation.org> In-Reply-To: <20210312210632.9b7d62973d72a56fb13c7a03@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: "Matthew Wilcox (Oracle)" Subject: include/linux/sched/mm.h: use rcu_dereference in in_vfork() Fix a sparse warning by using rcu_dereference(). Technically this is a bug and a sufficiently aggressive compiler could reload the `real_parent' pointer outside the protection of the rcu lock (and access freed memory), but I think it's pretty unlikely to happen. Link: https://lkml.kernel.org/r/20210221194207.1351703-1-willy@infradead.org Fixes: b18dc5f291c0 ("mm, oom: skip vforked tasks from being selected") Signed-off-by: Matthew Wilcox (Oracle) Reviewed-by: Miaohe Lin Acked-by: Michal Hocko Signed-off-by: Andrew Morton --- include/linux/sched/mm.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/include/linux/sched/mm.h~mm-use-rcu_dereference-in-in_vfork +++ a/include/linux/sched/mm.h @@ -140,7 +140,8 @@ static inline bool in_vfork(struct task_ * another oom-unkillable task does this it should blame itself. */ rcu_read_lock(); - ret = tsk->vfork_done && tsk->real_parent->mm == tsk->mm; + ret = tsk->vfork_done && + rcu_dereference(tsk->real_parent)->mm == tsk->mm; rcu_read_unlock(); return ret; _