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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C328CC4320A for ; Wed, 28 Jul 2021 16:43:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 77C6160F01 for ; Wed, 28 Jul 2021 16:43:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 77C6160F01 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id CA04A8D0002; 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Wed, 28 Jul 2021 16:43:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1627490588; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=03doPF0Hm9VX9+U1BaRb0OdFxpJZ53fMHg22McZ99ig=; b=eaol6RxXf7+m2YKwFbYesAbm4xgVs/1VQcxOfo++HD7LxE1zGg6ukvWgka8lVscyStIBep e6F0QMB3gKyfxylz7xo9HPQ0proQV82xTS1TyNw0T6g1c0hz0J+T4LZL2hYtLcrqG9dF85 db4KjKnW2o2SWDr5LuCOQWBurbOrTOs= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 918D4A3B83; Wed, 28 Jul 2021 16:43:07 +0000 (UTC) Date: Wed, 28 Jul 2021 18:43:07 +0200 From: Michal Hocko To: Shakeel Butt Cc: Roman Gushchin , Wang Hai , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Johannes Weiner , Alexei Starovoitov , wangkefeng.wang@huawei.com, Linux MM , LKML Subject: Re: [PATCH] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook() Message-ID: References: <20210728091348.272714-1-wanghai38@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C08F1B004ABB Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=eaol6RxX; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf25.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Stat-Signature: k4ut98h1au837mrkznimic5sosiawzaf X-HE-Tag: 1627490589-27494 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 28-07-21 07:10:26, Shakeel Butt wrote: > +Roman > > On Wed, Jul 28, 2021 at 6:23 AM 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 > > 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. > > Actually they are different. For MEMCG_DATA_KMEM page, > page_has_obj_cgroups() will return false while page_objcgs() on > non-VM_DEBUG kernels will return "struct obj_cgroup *" instead of > "struct obj_cgroup **". Right. Thanks for the clarification. I have missed that subtle difference. -- Michal Hocko SUSE Labs