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Wed, 28 Jul 2021 22:30:11 +0800 (CST) Received: from [10.174.176.245] (10.174.176.245) by dggeme766-chm.china.huawei.com (10.3.19.112) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Wed, 28 Jul 2021 22:33:56 +0800 Subject: Re: [PATCH] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook() To: Shakeel Butt , Kefeng Wang CC: Michal Hocko , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Johannes Weiner , Alexei Starovoitov , Linux MM , LKML References: <20210728091348.272714-1-wanghai38@huawei.com> From: "wanghai (M)" Message-ID: Date: Wed, 28 Jul 2021 22:33:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed X-Originating-IP: [10.174.176.245] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggeme766-chm.china.huawei.com (10.3.19.112) X-CFilter-Loop: Reflected X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: B9ED6D000F44 Authentication-Results: imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of wanghai38@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=wanghai38@huawei.com; dmarc=pass (policy=none) header.from=huawei.com X-Stat-Signature: 6uin5oh5k636t57ydxc34snfnwoc5gxm X-HE-Tag: 1627482839-127284 Content-Transfer-Encoding: quoted-printable 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: =E5=9C=A8 2021/7/28 22:26, Shakeel Butt =E5=86=99=E9=81=93: > On Wed, Jul 28, 2021 at 7:21 AM Kefeng Wang wrote: >> >> On 2021/7/28 21:23, Michal Hocko wrote: >>> On Wed 28-07-21 17:13:48, 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. >>>> >>>> So in this case, there is no need to do anything with this large >>>> page in memcg_slab_free_hook(), just skip it. >>>> >>>> Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access sla= b page's memcg_data") >>> Are you sure that this commit is really breaking the code. Unless I h= ave >> Yes, we confirmed that this commit introduces the bug. >>> missed something there shouldn't be any real change wrt. large >>> allocations here. page_has_obj_cgroups is just a different name for w= hat >>> what page_objcgs is giving us. >> maybe we could simply use page_objcgs_check to fix the issue ? we will >> check it again. > You will see the same crash with page_objcgs_check as well. > . I just test it. It won't crash. This is the test case: node =3D kmalloc_node(299999, GFP_ATOMIC | __GFP_NOWARN | __GFP_ACCOUNT, = -1); kfree_rcu(node, rcu);