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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 462B0C04AA5 for ; Thu, 25 Aug 2022 02:34:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 94710940008; Wed, 24 Aug 2022 22:34:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8F455940007; Wed, 24 Aug 2022 22:34:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7BCC2940008; Wed, 24 Aug 2022 22:34:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 6C00B940007 for ; Wed, 24 Aug 2022 22:34:24 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 42F5940F4D for ; Thu, 25 Aug 2022 02:34:24 +0000 (UTC) X-FDA: 79836546048.12.29D174C Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by imf15.hostedemail.com (Postfix) with ESMTP id 2CB2EA002A for ; Thu, 25 Aug 2022 02:34:23 +0000 (UTC) Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.57]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4MCn544Krgz19S4g; Thu, 25 Aug 2022 10:30:48 +0800 (CST) Received: from dggpemm500001.china.huawei.com (7.185.36.107) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 25 Aug 2022 10:34:19 +0800 Received: from [10.174.177.243] (10.174.177.243) by dggpemm500001.china.huawei.com (7.185.36.107) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 25 Aug 2022 10:34:18 +0800 Message-ID: Date: Thu, 25 Aug 2022 10:34:18 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH 2/2] mm: slince possible data races about pgdat->kswapd Content-Language: en-US To: David Hildenbrand , Andrew Morton , CC: , References: <20220824071909.192535-1-wangkefeng.wang@huawei.com> <20220824071909.192535-2-wangkefeng.wang@huawei.com> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of wangkefeng.wang@huawei.com designates 45.249.212.255 as permitted sender) smtp.mailfrom=wangkefeng.wang@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661394863; a=rsa-sha256; cv=none; b=zKL13v8+udXa3bWyHke7A743PeYIvHeNoU6FJv+95GN6Qrv6Y46zOphed7HMHOLS535WkZ OFLG5nyWxnEprvnFwpaHXpTb1JIcX5bzPotFamn0IWiIR/OgbiTVITtcBdfU4U5YuVkCV4 GNrCGyga20PunwkBidMgbDEphqsztUY= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661394863; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fo3n9MUx/soptTOolWVYKGS6Fxqg4oN94s04j6aUaNw=; b=WPqioVUbui2px9pLFO3xRANPsJBFt62DhvBZPdWvAEgf1R5vriKqcfymqM2UVCzQ+7oytl NGfEcP1xgqG+hr9uImg4wm7PAlJQ994pRzSC70sCweees4qMycqUMBDXMq2mLEUqFA7sjU SbR2UDgiCrTLJc2kvJDpYC/R9rYJNt0= Authentication-Results: imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of wangkefeng.wang@huawei.com designates 45.249.212.255 as permitted sender) smtp.mailfrom=wangkefeng.wang@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Stat-Signature: p9aq1akbpgz18ha135qk41tha7bcjzia X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 2CB2EA002A X-Rspam-User: X-HE-Tag: 1661394863-45820 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: On 2022/8/24 16:24, David Hildenbrand wrote: > On 24.08.22 09:19, Kefeng Wang wrote: >> The pgdat->kswapd could be accessed concurrently by kswapd_run() and >> kcompactd(), it don't be protected by any lock, which could leads to >> data races, adding READ/WRITE_ONCE() to slince it. > Okay, I think this patch here makes it clearer that we really just want > proper synchronization instead of hacking around it. > > What speaks against protecting pgdat->kswapd this using some proper > locking primitive? as comments about kswapd in struct pglist_data,  pgdat->kswapd should be protected by mem_hotplug_begin/done(), how about this way? diff --git a/mm/compaction.c b/mm/compaction.c index 640fa76228dd..62018f35242a 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1983,7 +1983,13 @@ static inline bool is_via_compact_memory(int order)  static bool kswapd_is_running(pg_data_t *pgdat)  { -       return pgdat->kswapd && task_is_running(pgdat->kswapd); +       bool running; + +       mem_hotplug_begin(); +       running = pgdat->kswapd && task_is_running(pgdat->kswapd); +       mem_hotplug_end(); + +       return running;  }