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 CEB39ECAAA2 for ; Mon, 29 Aug 2022 01:38:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A258B940008; Sun, 28 Aug 2022 21:38:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9D458940007; Sun, 28 Aug 2022 21:38:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 84E31940008; Sun, 28 Aug 2022 21:38:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 70402940007 for ; Sun, 28 Aug 2022 21:38:18 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 44ACE1202C1 for ; Mon, 29 Aug 2022 01:38:18 +0000 (UTC) X-FDA: 79850919876.11.B55ECCE Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf27.hostedemail.com (Postfix) with ESMTP id 64A724005F for ; Mon, 29 Aug 2022 01:38:16 +0000 (UTC) Received: from dggpemm500020.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4MGCgm3gwVznTW1; Mon, 29 Aug 2022 09:35:48 +0800 (CST) Received: from dggpemm500001.china.huawei.com (7.185.36.107) by dggpemm500020.china.huawei.com (7.185.36.49) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 29 Aug 2022 09:38:12 +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; Mon, 29 Aug 2022 09:38:12 +0800 Message-ID: <271c1983-9f84-46ee-4c9f-beb1aa3a681f@huawei.com> Date: Mon, 29 Aug 2022 09:38:11 +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 v2] mm: fix null-ptr-deref in kswapd_is_running() Content-Language: en-US To: Andrew Morton CC: , , David Hildenbrand , Muchun Song References: <20220827111959.186838-1-wangkefeng.wang@huawei.com> <20220827150855.b8885a5c4f09df712d619760@linux-foundation.org> From: Kefeng Wang In-Reply-To: <20220827150855.b8885a5c4f09df712d619760@linux-foundation.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661737097; a=rsa-sha256; cv=none; b=keHUEcIreZO7+SclDMTkTPROmwhE1jId9xFoyyaSycdl/ERgyAbXr6qniBREKvpOGS+t+2 4xP7cIb8pH+X0Ov7UF4tPAhZzB+YGNBdq5V1uE2DTYFRVzAwo6lwGS9YUOL3AH95g23anC E8RlHvKZAXS7tV7vfV76PO9Dp7MLxhw= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf27.hostedemail.com: domain of wangkefeng.wang@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=wangkefeng.wang@huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661737097; 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=M5E2kZ/NUlCqAkks/vFO+5hvzoMYjcT2HVlmzSriSDk=; b=p5O5xmxV0i+tLbpvQtEmorP78mUIIkQ0SC6nTGdD4IVffpSOphjR2+TTf/KzbvyNt+YvR1 IB4aM3iVvyL9O4zc+T2ofnphrU250iNatt7MtsgXWItHPlP8usDepvyuWTm5P7iFLqwh4G i9QBF2QTv6LvaeXoNrgaKOAEyewGZ3s= Authentication-Results: imf27.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf27.hostedemail.com: domain of wangkefeng.wang@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=wangkefeng.wang@huawei.com X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 64A724005F X-Stat-Signature: ade5zukxognufw1ri7mk1a5p5j19n5ai X-HE-Tag: 1661737096-639507 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 2022/8/28 6:08, Andrew Morton wrote: > On Sat, 27 Aug 2022 19:19:59 +0800 Kefeng Wang wrote: > >> The kswapd_run/stop() will set pgdat->kswapd to NULL, which >> could race with kswapd_is_running() in kcompactd(), >> >> kswapd_run/stop() kcompactd() >> kswapd_is_running() >> pgdat->kswapd // error or nomal ptr >> verify pgdat->kswapd >> // load non-NULL >> pgdat->kswapd >> pgdat->kswapd = NULL >> task_is_running(pgdat->kswapd) >> // Null pointer derefence >> >> The KASAN report the null-ptr-deref shown below, >> >> vmscan: Failed to start kswapd on node 0 >> ... >> BUG: KASAN: null-ptr-deref in kcompactd+0x440/0x504 >> Read of size 8 at addr 0000000000000024 by task kcompactd0/37 >> >> CPU: 0 PID: 37 Comm: kcompactd0 Kdump: loaded Tainted: G OE 5.10.60 #1 >> Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 >> Call trace: >> dump_backtrace+0x0/0x394 >> show_stack+0x34/0x4c >> dump_stack+0x158/0x1e4 >> __kasan_report+0x138/0x140 >> kasan_report+0x44/0xdc >> __asan_load8+0x94/0xd0 >> kcompactd+0x440/0x504 >> kthread+0x1a4/0x1f0 >> ret_from_fork+0x10/0x18 >> >> For now, kswapd/kcompactd_run() and kswapd/kcompactd_stop() protected >> by mem_hotplug_begin/done(), but without kcompactd(). It is no need to >> involve memory hotplug lock in kcompactd(), so let's add new mutex to >> protect pgdat->kswapd accessed concurrently, also because kcompactd task >> will check the state of kswapd task, it's better to call kcompactd_stop() >> before kswapd_stop() to reduce lock conflicts. >> > Looks right to me. > > I think the below will make the code a little more maintainable? Thanks Andrew, it's better. > > --- a/include/linux/memory_hotplug.h~mm-fix-null-ptr-deref-in-kswapd_is_running-fix > +++ a/include/linux/memory_hotplug.h > @@ -215,6 +215,7 @@ void put_online_mems(void); > void mem_hotplug_begin(void); > void mem_hotplug_done(void); > > +/* See kswapd_is_running() */ > static inline void pgdat_kswapd_lock(pg_data_t *pgdat) > { > mutex_lock(&pgdat->kswapd_lock); > --- a/mm/compaction.c~mm-fix-null-ptr-deref-in-kswapd_is_running-fix > +++ a/mm/compaction.c > @@ -1980,6 +1980,12 @@ static inline bool is_via_compact_memory > return order == -1; > } > > +/* > + * Determine whether kswapd is (or recently was!) running on this node. > + * > + * pgdat_kswapd_lock() pins pgdat->kswapd, so a concurrent kswapd_stop() can't > + * zero it. > + */ > static bool kswapd_is_running(pg_data_t *pgdat) > { > bool running; > _ > > .