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=-17.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,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 06640C07E96 for ; Thu, 8 Jul 2021 11:50:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D924E61440 for ; Thu, 8 Jul 2021 11:50:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231774AbhGHLw6 (ORCPT ); Thu, 8 Jul 2021 07:52:58 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:6768 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231628AbhGHLw5 (ORCPT ); Thu, 8 Jul 2021 07:52:57 -0400 Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4GLDwq3J4bzXqTX; Thu, 8 Jul 2021 19:44:43 +0800 (CST) Received: from huawei.com (10.175.124.27) by dggeme703-chm.china.huawei.com (10.1.199.99) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Thu, 8 Jul 2021 19:50:13 +0800 From: Miaohe Lin To: , , CC: , , , Subject: [PATCH v2] mm/zsmalloc.c: close race window between zs_pool_dec_isolated() and zs_unregister_migration() Date: Thu, 8 Jul 2021 19:50:27 +0800 Message-ID: <20210708115027.7557-1-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.124.27] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There has one possible race window between zs_pool_dec_isolated() and zs_unregister_migration() because wait_for_isolated_drain() checks the isolated count without holding class->lock and there is no order inside zs_pool_dec_isolated(). Thus the below race window could be possible: zs_pool_dec_isolated zs_unregister_migration check pool->destroying != 0 pool->destroying = true; smp_mb(); wait_for_isolated_drain() wait for pool->isolated_pages == 0 atomic_long_dec(&pool->isolated_pages); atomic_long_read(&pool->isolated_pages) == 0 Since we observe the pool->destroying (false) before atomic_long_dec() for pool->isolated_pages, waking pool->migration_wait up is missed. Fix this by ensure checking pool->destroying is happened after the atomic_long_dec(&pool->isolated_pages). Fixes: 701d678599d0 ("mm/zsmalloc.c: fix race condition in zs_destroy_pool") Signed-off-by: Miaohe Lin --- v1->v2: Fix potential race window rather than simply combine atomic_long_dec and atomic_long_read. Hi Andrew, This patch is the version 2 of mm-zsmallocc-combine-two-atomic-ops-in-zs_pool_dec_isolated.patch. Many thanks. --- mm/zsmalloc.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 5f3df680f0a2..0fc388a0202d 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1830,10 +1830,11 @@ static inline void zs_pool_dec_isolated(struct zs_pool *pool) VM_BUG_ON(atomic_long_read(&pool->isolated_pages) <= 0); atomic_long_dec(&pool->isolated_pages); /* - * There's no possibility of racing, since wait_for_isolated_drain() - * checks the isolated count under &class->lock after enqueuing - * on migration_wait. + * Checking pool->destroying must happen after atomic_long_dec() + * for pool->isolated_pages above. Paired with the smp_mb() in + * zs_unregister_migration(). */ + smp_mb__after_atomic(); if (atomic_long_read(&pool->isolated_pages) == 0 && pool->destroying) wake_up_all(&pool->migration_wait); } -- 2.23.0