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Wed, 28 Jul 2021 23:32:43 +0000 Date: Wed, 28 Jul 2021 16:32:41 -0700 From: Roman Gushchin To: Michal Hocko CC: Wang Hai , , , , , , , , , , , , Subject: Re: [PATCH v2] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook() Message-ID: References: <20210728145655.274476-1-wanghai38@huawei.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: SJ0PR03CA0204.namprd03.prod.outlook.com (2603:10b6:a03:2ef::29) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.lan (2620:10d:c090:400::5:d9b0) by SJ0PR03CA0204.namprd03.prod.outlook.com (2603:10b6:a03:2ef::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4373.18 via Frontend Transport; Wed, 28 Jul 2021 23:32:43 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: f3e16a84-34bb-47d9-066f-08d9521fff8e X-MS-TrafficTypeDiagnostic: SJ0PR15MB4598: X-Microsoft-Antispam-PRVS: X-FB-Source: Internal X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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dkim=pass header.d=fb.com header.s=facebook header.b=lgJtaL7Q; dmarc=pass (policy=reject) header.from=fb.com; spf=pass (imf11.hostedemail.com: domain of "prvs=78431cb8f7=guro@fb.com" designates 67.231.153.30 as permitted sender) smtp.mailfrom="prvs=78431cb8f7=guro@fb.com" X-Stat-Signature: ygytatnjqqoh99qsy84569ij436f3hbh X-HE-Tag: 1627515188-504475 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 Wed, Jul 28, 2021 at 06:44:03PM +0200, Michal Hocko wrote: > On Wed 28-07-21 22:56:55, Wang Hai wrote: > > When I use kfree_rcu() to free a large memory allocated by > > kmalloc_node(), the following dump occurs. > > > > BUG: kernel NULL pointer dereference, address: 0000000000000020 > > [...] > > Oops: 0000 [#1] SMP > > [...] > > Workqueue: events kfree_rcu_work > > RIP: 0010:__obj_to_index include/linux/slub_def.h:182 [inline] > > RIP: 0010:obj_to_index include/linux/slub_def.h:191 [inline] > > RIP: 0010:memcg_slab_free_hook+0x120/0x260 mm/slab.h:363 > > [...] > > Call Trace: > > kmem_cache_free_bulk+0x58/0x630 mm/slub.c:3293 > > kfree_bulk include/linux/slab.h:413 [inline] > > kfree_rcu_work+0x1ab/0x200 kernel/rcu/tree.c:3300 > > process_one_work+0x207/0x530 kernel/workqueue.c:2276 > > worker_thread+0x320/0x610 kernel/workqueue.c:2422 > > kthread+0x13d/0x160 kernel/kthread.c:313 > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 > > > > When kmalloc_node() a large memory, page is allocated, not slab, > > so when freeing memory via kfree_rcu(), this large memory should not > > be used by memcg_slab_free_hook(), because memcg_slab_free_hook() is > > is used for slab. > > > > Using page_objcgs_check() instead of page_objcgs() in > > memcg_slab_free_hook() to fix this bug. > > > > Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data") > > Signed-off-by: Wang Hai > > This looks like a much better fix. Thanks! +1 Acked-by: Roman Gushchin Thank you, Wang!