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=-15.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 ACFE6C07E96 for ; Thu, 8 Jul 2021 12:14:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2011361580 for ; Thu, 8 Jul 2021 12:14:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2011361580 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D4BF96B006C; Thu, 8 Jul 2021 08:14:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CFB276B0070; Thu, 8 Jul 2021 08:14:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BC2BD6B0071; Thu, 8 Jul 2021 08:14:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id 995D76B006C for ; Thu, 8 Jul 2021 08:14:46 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id E9461284A6 for ; Thu, 8 Jul 2021 12:14:45 +0000 (UTC) X-FDA: 78339314130.01.EF4E3CA Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf13.hostedemail.com (Postfix) with ESMTP id DCDCC1003ED6 for ; Thu, 8 Jul 2021 12:14:40 +0000 (UTC) Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4GLFW62Z6Kz798P; Thu, 8 Jul 2021 20:10:58 +0800 (CST) Received: from [10.174.177.209] (10.174.177.209) 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 20:14:26 +0800 Subject: Re: [PATCH v2] mm/zsmalloc.c: close race window between zs_pool_dec_isolated() and zs_unregister_migration() To: , , CC: , , , References: <20210708115117.12359-1-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <7a16cf45-eaed-e7ba-bf47-2382b2c542f2@huawei.com> Date: Thu, 8 Jul 2021 20:14:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210708115117.12359-1-linmiaohe@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.209] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected X-Stat-Signature: xawusss5iap1tfpaeyzdmwx5qwr69je7 X-Rspamd-Queue-Id: DCDCC1003ED6 X-Rspamd-Server: rspam01 X-Rspam-User: nil Authentication-Results: imf13.hostedemail.com; dkim=none; spf=pass (imf13.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=none) header.from=huawei.com X-HE-Tag: 1625746480-172629 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Sorry for the disturbs! Please ignore this duplicated one... On 2021/7/8 19:51, Miaohe Lin wrote: > 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); > } >