From nobody Fri Apr 10 18:36:55 2026 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 E6927C25B08 for ; Sat, 20 Aug 2022 03:19:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244159AbiHTDTn (ORCPT ); Fri, 19 Aug 2022 23:19:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43402 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244019AbiHTDTh (ORCPT ); Fri, 19 Aug 2022 23:19:37 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A12E356BA4 for ; Fri, 19 Aug 2022 20:19:34 -0700 (PDT) Received: from dggpemm500020.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4M8kMn0dGyzGpfF; Sat, 20 Aug 2022 11:17:57 +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; Sat, 20 Aug 2022 11:19:32 +0800 Received: from localhost.localdomain.localdomain (10.175.113.25) 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; Sat, 20 Aug 2022 11:19:31 +0800 From: Kefeng Wang To: Andrew Morton , CC: Qian Cai , , Kefeng Wang Subject: [PATCH] mm: fix pgdat->kswap accessed concurrently Date: Sat, 20 Aug 2022 11:25:06 +0800 Message-ID: <20220820032506.126860-1-wangkefeng.wang@huawei.com> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.175.113.25] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The pgdat->kswap could be accessed concurrently by kswapd_run() and kcompactd(), it don't be protected by any lock, which leads to the following null-ptr-deref, 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 Fix it by adding READ_ONCE()|WRITE_ONCE(). Signed-off-by: Kefeng Wang Reviewed-by: Muchun Song --- mm/compaction.c | 4 +++- mm/vmscan.c | 15 +++++++++------ 2 files changed, 12 insertions(+), 7 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 640fa76228dd..aa1cfe47f046 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1983,7 +1983,9 @@ static inline bool is_via_compact_memory(int order) =20 static bool kswapd_is_running(pg_data_t *pgdat) { - return pgdat->kswapd && task_is_running(pgdat->kswapd); + struct task_struct *t =3D READ_ONCE(pgdat->kswapd); + + return t && task_is_running(t); } =20 /* diff --git a/mm/vmscan.c b/mm/vmscan.c index b2b1431352dc..9abba714249e 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4642,16 +4642,19 @@ unsigned long shrink_all_memory(unsigned long nr_to= _reclaim) void kswapd_run(int nid) { pg_data_t *pgdat =3D NODE_DATA(nid); + struct task_struct *t; =20 - if (pgdat->kswapd) + if (READ_ONCE(pgdat->kswapd)) return; =20 - pgdat->kswapd =3D kthread_run(kswapd, pgdat, "kswapd%d", nid); - if (IS_ERR(pgdat->kswapd)) { + t =3D kthread_run(kswapd, pgdat, "kswapd%d", nid); + if (IS_ERR(t)) { /* failure at boot is fatal */ BUG_ON(system_state < SYSTEM_RUNNING); pr_err("Failed to start kswapd on node %d\n", nid); - pgdat->kswapd =3D NULL; + WRITE_ONCE(pgdat->kswapd, NULL); + } else { + WRITE_ONCE(pgdat->kswapd, t); } } =20 @@ -4661,11 +4664,11 @@ void kswapd_run(int nid) */ void kswapd_stop(int nid) { - struct task_struct *kswapd =3D NODE_DATA(nid)->kswapd; + struct task_struct *kswapd =3D READ_ONCE(NODE_DATA(nid)->kswapd); =20 if (kswapd) { kthread_stop(kswapd); - NODE_DATA(nid)->kswapd =3D NULL; + WRITE_ONCE(NODE_DATA(nid)->kswapd, NULL); } } =20 --=20 2.35.3