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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 A431BC4338F for ; Wed, 28 Jul 2021 13:23:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83FCF6101D for ; Wed, 28 Jul 2021 13:23:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235942AbhG1NXP (ORCPT ); Wed, 28 Jul 2021 09:23:15 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:47410 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233315AbhG1NXO (ORCPT ); Wed, 28 Jul 2021 09:23:14 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 66B701FFC7; Wed, 28 Jul 2021 13:23:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1627478592; 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=WJzhKiA6oIO7oLr1sdiTWSyxqi+PYk7isJPGsfi89Go=; b=BueN44Ims3KQNM4UoedO8pW733T5e1CfQYF/8Bkp666xKg84qoe5vF47ZyKlVW1wT49YME zUVwGC7MbD5tDJXwTmloiqXIdv03OakhWUw+eVjXZqX/3Lep9JeHQxKkiMqmLRjPkKSV+C W/OPYCWMAcpSdRJE+2+BKjOPUu69usc= 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 E3AF3A3B8E; Wed, 28 Jul 2021 13:23:11 +0000 (UTC) Date: Wed, 28 Jul 2021 15:23:11 +0200 From: Michal Hocko To: Wang Hai Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, hannes@cmpxchg.org, shakeelb@google.com, ast@kernel.org, wangkefeng.wang@huawei.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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: <20210728091348.272714-1-wanghai38@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. I haven't studied the kfree_rcu part but isn't the problem its use of kmem_cache_free_bulk or isn't the problem right there in the bulk free? > Signed-off-by: Wang Hai > --- > mm/slab.h | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 67e06637ff2e..247d3f9c21f7 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -339,15 +339,20 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig, > continue; > > page = virt_to_head_page(p[i]); > + if (!s_orig) { > + if (unlikely(!PageSlab(page))) { > + BUG_ON(!PageCompound(page)); BUG_ON is not really a good idea here. Why should we crash the kernel just because of an unexpected page showing up. Leaking it would be more appropriate (the same would apply to kfree btw). I would just warn here. Also don't we need any hookd here. Looking at kfree path it does call kfree_hook. Why is that not needed here? > + continue; > + } > + s = page->slab_cache; > + } else { > + s = s_orig; > + } > + > objcgs = page_objcgs(page); > if (!objcgs) > continue; > > - if (!s_orig) > - s = page->slab_cache; > - else > - s = s_orig; > - > off = obj_to_index(s, page, p[i]); > objcg = objcgs[off]; > if (!objcg) > -- > 2.17.1 -- Michal Hocko SUSE Labs