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=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,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 AD1BFC2D0AE for ; Tue, 13 Oct 2020 23:53:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66841221FF for ; Tue, 13 Oct 2020 23:53:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602633203; bh=Q8HLFTATOkI/j2bnsqR01lRU60IVX6GDxAjATU7vDA8=; h=Date:From:To:Subject:In-Reply-To:Reply-To:List-ID:From; b=o/8OnGHvXbzXnR6t3SfNfs8CcKKn24hWlIzAMCjLFpIJKvPnm9fqzcYOb2Crcvlnx AWnrIyuLvI7/9ISC9NV7XXNZOj0aNZMxXG15LSeAzK2zSeIMfmT+2V11TOVJgSuMkS 3WBkdt+EBcx+VLSgHX2O9NXnensEvRn80DXErmOo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730122AbgJMXxW (ORCPT ); Tue, 13 Oct 2020 19:53:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:37644 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729212AbgJMXwn (ORCPT ); Tue, 13 Oct 2020 19:52:43 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 078CC22202; Tue, 13 Oct 2020 23:52:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602633163; bh=Q8HLFTATOkI/j2bnsqR01lRU60IVX6GDxAjATU7vDA8=; h=Date:From:To:Subject:In-Reply-To:From; b=070k21cq674eaFGn+6G8dJyCdGLINFTJVfodsU60aICo1FTEXMO3P8x766ZTKI1/l q6e085SPYNnkeennIA4NUf/6oH/6iR9+uPrDfmo3VZa9hQQVTpukI8o3aIJ4JpvZwt 6cJWOApWJ7c2ZJY2T1vdjHFQQgN9mAG8Scoqv9/s= Date: Tue, 13 Oct 2020 16:52:42 -0700 From: Andrew Morton To: akpm@linux-foundation.org, guro@fb.com, hannes@cmpxchg.org, linux-mm@kvack.org, mm-commits@vger.kernel.org, shakeelb@google.com, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 080/181] mm: memcg/slab: fix racy access to page->mem_cgroup in mem_cgroup_from_obj() Message-ID: <20201013235242.2aU4e1EVF%akpm@linux-foundation.org> In-Reply-To: <20201013164658.3bfd96cc224d8923e66a9f4e@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Roman Gushchin Subject: mm: memcg/slab: fix racy access to page->mem_cgroup in mem_cgroup_from_obj() mem_cgroup_from_obj() checks the lowest bit of the page->mem_cgroup pointer to determine if the page has an attached obj_cgroup vector instead of a regular memcg pointer. If it's not set, it simple returns the page->mem_cgroup value as a struct mem_cgroup pointer. The commit 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches for all allocations") changed the moment when this bit is set: if previously it was set on the allocation of the slab page, now it can be set well after, when the first accounted object is allocated on this page. It opened a race: if page->mem_cgroup is set concurrently after the first page_has_obj_cgroups(page) check, a pointer to the obj_cgroups array can be returned as a memory cgroup pointer. A simple check for page->mem_cgroup pointer for NULL before the page_has_obj_cgroups() check fixes the race. Indeed, if the pointer is not NULL, it's either a simple mem_cgroup pointer or a pointer to obj_cgroup vector. The pointer can be asynchronously changed from NULL to (obj_cgroup_vec | 0x1UL), but can't be changed from a valid memcg pointer to objcg vector or back. If the object passed to mem_cgroup_from_obj() is a slab object and page->mem_cgroup is NULL, it means that the object is not accounted, so the function must return NULL. I've discovered the race looking at the code, so far I haven't seen it in the wild. Link: https://lkml.kernel.org/r/20200910022435.2773735-1-guro@fb.com Fixes: 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches for all allocations") Signed-off-by: Roman Gushchin Reviewed-by: Shakeel Butt Cc: Johannes Weiner Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/memcontrol.c | 11 +++++++++++ 1 file changed, 11 insertions(+) --- a/mm/memcontrol.c~mm-memcg-slab-fix-racy-access-to-page-mem_cgroup-in-mem_cgroup_from_obj +++ a/mm/memcontrol.c @@ -2888,6 +2888,17 @@ struct mem_cgroup *mem_cgroup_from_obj(v page = virt_to_head_page(p); /* + * If page->mem_cgroup is set, it's either a simple mem_cgroup pointer + * or a pointer to obj_cgroup vector. In the latter case the lowest + * bit of the pointer is set. + * The page->mem_cgroup pointer can be asynchronously changed + * from NULL to (obj_cgroup_vec | 0x1UL), but can't be changed + * from a valid memcg pointer to objcg vector or back. + */ + if (!page->mem_cgroup) + return NULL; + + /* * Slab objects are accounted individually, not per-page. * Memcg membership data for each individual object is saved in * the page->obj_cgroups. _