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Wed, 28 Jul 2021 07:26:30 -0700 (PDT) MIME-Version: 1.0 References: <20210728091348.272714-1-wanghai38@huawei.com> In-Reply-To: From: Shakeel Butt Date: Wed, 28 Jul 2021 07:26:19 -0700 Message-ID: Subject: Re: [PATCH] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook() To: Kefeng Wang Cc: Michal Hocko , Wang Hai , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Johannes Weiner , Alexei Starovoitov , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=lauEEuiR; spf=pass (imf11.hostedemail.com: domain of shakeelb@google.com designates 209.85.208.177 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam02 X-Stat-Signature: t8frfn9gwm4a5fxgyh5g8ccszfnxiriz X-Rspamd-Queue-Id: 8CEB0F0081E8 X-HE-Tag: 1627482392-558282 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 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 slab page's memcg_data") > > Are you sure that this commit is really breaking the code. Unless I have > 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 what > > 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.