From patchwork Wed Dec 28 17:59:42 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13083090 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 4A4EAC3DA7D for ; Wed, 28 Dec 2022 17:59:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230443AbiL1R7u (ORCPT ); Wed, 28 Dec 2022 12:59:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46748 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233083AbiL1R7t (ORCPT ); Wed, 28 Dec 2022 12:59:49 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F25CA167C0; Wed, 28 Dec 2022 09:59:46 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 979C86158F; Wed, 28 Dec 2022 17:59:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E0E9C433F0; Wed, 28 Dec 2022 17:59:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1672250386; bh=XN9PcsyPPRLwqqgJ2SzuIm7xkFHpLYHw7zI07sgsjnc=; h=From:To:Cc:Subject:Date:From; b=dnUZukkc3qKrGLW6R3tkbIKWiwATzVWetlE/iWL6Rx7JJJPCfkJwdj4arTf88CmpJ 7x6mJ27NRKW3BVc8h6cFtsmTUDQEXuUfiUfOdPZ5rmDjibNxqU1i7mqALaVvVtm14P C4hIDOdP5gRo7cHXKrqo3WL91/3iPq88gTKW4496/wH26+Uj7SSYLjSnwfEfotIkmX X7WsfiIvsHrrWDi5HBibzsJKnpQ9s4dlQFlaxGf8wxHrRwf4EyT6wmpRaeLOllAv1a 2QHnGEQiBAKMl0ORqgWjckrysWHXHC5zj+/WzOnmuJsMK2gnbLzCapjL8Qk105IqjH sL4vkh84YjfGQ== From: SeongJae Park To: akpm@linux-foundation.org Cc: SeongJae Park , alexander.h.duyck@linux.intel.com, willy@infradead.org, linmiaohe@huawei.com, linux-mm@kvack.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3] mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected() Date: Wed, 28 Dec 2022 17:59:42 +0000 Message-Id: <20221228175942.149491-1-sj@kernel.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Page reporting fetches pr_dev_info using rcu_access_pointer(), which is for safely fetching a pointer that will not be dereferenced but could concurrently updated. The code indeed does not dereference pr_dev_info after fetching it using rcu_access_pointer(), but it fetches the pointer while concurrent updates to the pointer is avoided by holding the update side lock, page_reporting_mutex. In the case, rcu_dereference_protected() should be used instead because it provides better readability and performance on some cases, as rcu_dereference_protected() avoids use of READ_ONCE(). Replace the rcu_access_pointer() calls with rcu_dereference_protected(). Fixes: 36e66c554b5c ("mm: introduce Reported pages") Signed-off-by: SeongJae Park --- Changes from v2 (https://lore.kernel.org/linux-mm/20221228012902.1510901-1-sj@kernel.org/) - Fix typos (Miaohe Lin) - Add Fixes: tag Changes from v1 (https://lore.kernel.org/linux-mm/20221227192158.2553-1-sj@kernel.org/) - Explicitly set the protection condition (Matthew Wilcox) mm/page_reporting.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/page_reporting.c b/mm/page_reporting.c index 79a8554f024c..c65813a9dc78 100644 --- a/mm/page_reporting.c +++ b/mm/page_reporting.c @@ -356,7 +356,8 @@ int page_reporting_register(struct page_reporting_dev_info *prdev) mutex_lock(&page_reporting_mutex); /* nothing to do if already in use */ - if (rcu_access_pointer(pr_dev_info)) { + if (rcu_dereference_protected(pr_dev_info, + lockdep_is_held(&page_reporting_mutex))) { err = -EBUSY; goto err_out; } @@ -401,7 +402,8 @@ void page_reporting_unregister(struct page_reporting_dev_info *prdev) { mutex_lock(&page_reporting_mutex); - if (rcu_access_pointer(pr_dev_info) == prdev) { + if (prdev == rcu_dereference_protected(pr_dev_info, + lockdep_is_held(&page_reporting_mutex))) { /* Disable page reporting notification */ RCU_INIT_POINTER(pr_dev_info, NULL); synchronize_rcu();