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=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 C59E2C433B4 for ; Wed, 31 Mar 2021 13:54:23 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 432FF60725 for ; Wed, 31 Mar 2021 13:54:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 432FF60725 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id AC8956B007D; Wed, 31 Mar 2021 09:54:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A9F9E6B0081; Wed, 31 Mar 2021 09:54:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 940A36B0082; Wed, 31 Mar 2021 09:54:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0173.hostedemail.com [216.40.44.173]) by kanga.kvack.org (Postfix) with ESMTP id 78E6C6B007D for ; Wed, 31 Mar 2021 09:54:22 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 3D8B18124 for ; Wed, 31 Mar 2021 13:54:22 +0000 (UTC) X-FDA: 77980313964.08.5B8193C Received: from mail-lf1-f49.google.com (mail-lf1-f49.google.com [209.85.167.49]) by imf01.hostedemail.com (Postfix) with ESMTP id 70A445001530 for ; Wed, 31 Mar 2021 13:54:21 +0000 (UTC) Received: by mail-lf1-f49.google.com with SMTP id m12so29260745lfq.10 for ; Wed, 31 Mar 2021 06:54:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=M20/VCOtGm0wXrWdqbwDrpizR1Dl5NS3bwcYm8AfBw0=; b=Dmb/bo8n0TvTwTqvv+NggtHFmU26ULnHXF6bdDCQRkL2HMOZFaMk0XDclLGuOskS3G bWuXcCDsxFEmGFCl9Ix25HuGDrMNnXhnx/aWsFP90/pLWJHc4WztjoR0AlvunXVl/6br af6aRI7QNlTFBwVsXe+ciqvHgLSbF/EpOS2ccMrGPWnyoXFqeV0xlbGCMQOflfSJjHlN Qo2whdzp/tFx7d6mNS8YjpoQsFygLyPVnVMzsTLDPW+JDlZph+c3aQiEWdPIV9xiFAbj kppxBPPL7gUb0P/ylW9t80Ll3WstxyPO63vU4FUMD4gEfblM7W8IiLOIcclPypMylhzR uJ9w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=M20/VCOtGm0wXrWdqbwDrpizR1Dl5NS3bwcYm8AfBw0=; b=M5xFt6d4fUSHhmikcKewN2xsEMkMtsj2u21wdhxtHwIGlzVpfIzJb1kvMXyc6J9GS7 Q7iXig0b8ohaBzM/BTbNdxoXCojs4M4AOXHKbDJiLZTnb3YhO8uUoVGkwP6wND8bZsSo IWtFeagnwyssJpsp9hmAk+mISO26dTg0wt66hz4FlYGlIZ/FeE3IJBGzGf7zz7fniAbc yD6ivwynE3SLtzY/jzfE/yB7xI/KpOHOJ31x7d8OHatX0Z5XBzuc4r6lmOA9UBqyUyAr FQA5N0s6JqTZhYwSKQu/Scv6nVDn3XL3JN8mVul6cQJeyfGQ/c5FjfYn6gzKHuRxPwlY SCMA== X-Gm-Message-State: AOAM530BLqMslCqJWAxRdTas7ErzEmwAhDo8EScLi09KmUhtpWG0iXFg WSZ60aM1d7U0W8NJxoEJ995JAMRy33exkhGXLLS3XA== X-Google-Smtp-Source: ABdhPJzeXsNR6T8Lq37UZOq7zWxy4lmIQi5Lp1vf1OSrhYqss+SoiE8HkxZnCwPEf11EZ0RnzRVq60H/hEDpmagnS0k= X-Received: by 2002:a19:c14a:: with SMTP id r71mr2302682lff.358.1617198860128; Wed, 31 Mar 2021 06:54:20 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Shakeel Butt Date: Wed, 31 Mar 2021 06:54:08 -0700 Message-ID: Subject: Re: [PATCH mmotm] mm: vmscan: fix shrinker_rwsem in free_shrinker_info() To: Hugh Dickins Cc: Andrew Morton , kernel test robot , Yang Shi , Stephen Rothwell , Roman Gushchin , Kirill Tkhai , Vlastimil Babka , Dave Chinner , Johannes Weiner , Michal Hocko , LKML , Linux Memory Management List , lkp@lists.01.org, kernel test robot Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 70A445001530 X-Stat-Signature: d7s5ax6bmzjf1psghcjoniszidnr6wey X-Rspamd-Server: rspam02 Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf01; identity=mailfrom; envelope-from=""; helo=mail-lf1-f49.google.com; client-ip=209.85.167.49 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617198861-927709 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 Tue, Mar 30, 2021 at 4:44 PM Hugh Dickins wrote: > > Lockdep warns mm/vmscan.c: suspicious rcu_dereference_protected() usage! > when free_shrinker_info() is called from mem_cgroup_css_free(): there it > is called with no locking, whereas alloc_shrinker_info() calls it with > down_write of shrinker_rwsem - which seems appropriate. Rearrange that > so free_shrinker_info() can manage the shrinker_rwsem for itself. > > Link: https://lkml.kernel.org/r/20210317140615.GB28839@xsang-OptiPlex-9020 > Reported-by: kernel test robot > Signed-off-by: Hugh Dickins > Cc: Yang Shi > --- > Sorry, I've made no attempt to work out precisely where in the series > the locking went missing, nor tried to fit this in as a fix on top of > mm-vmscan-add-shrinker_info_protected-helper.patch > which Oliver reported (and which you notated in mmotm's "series" file). > This patch just adds the fix to the end of the series, after > mm-vmscan-shrink-deferred-objects-proportional-to-priority.patch The patch "mm: vmscan: add shrinker_info_protected() helper" replaces rcu_dereference_protected(shrinker_info, true) with rcu_dereference_protected(shrinker_info, lockdep_is_held(&shrinker_rwsem)). I think we don't really need shrinker_rwsem in free_shrinker_info() which is called from css_free(). The bits of the map have already been 'reparented' in css_offline. I think we can remove lockdep_is_held(&shrinker_rwsem) for free_shrinker_info(). > > mm/vmscan.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > --- mmotm/mm/vmscan.c 2021-03-28 17:26:54.935553064 -0700 > +++ linux/mm/vmscan.c 2021-03-30 15:55:13.374459559 -0700 > @@ -249,18 +249,20 @@ void free_shrinker_info(struct mem_cgrou > struct shrinker_info *info; > int nid; > > + down_write(&shrinker_rwsem); > for_each_node(nid) { > pn = memcg->nodeinfo[nid]; > info = shrinker_info_protected(memcg, nid); > kvfree(info); > rcu_assign_pointer(pn->shrinker_info, NULL); > } > + up_write(&shrinker_rwsem); > } > > int alloc_shrinker_info(struct mem_cgroup *memcg) > { > struct shrinker_info *info; > - int nid, size, ret = 0; > + int nid, size; > int map_size, defer_size = 0; > > down_write(&shrinker_rwsem); > @@ -270,9 +272,9 @@ int alloc_shrinker_info(struct mem_cgrou > for_each_node(nid) { > info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid); > if (!info) { > + up_write(&shrinker_rwsem); > free_shrinker_info(memcg); > - ret = -ENOMEM; > - break; > + return -ENOMEM; > } > info->nr_deferred = (atomic_long_t *)(info + 1); > info->map = (void *)info->nr_deferred + defer_size; > @@ -280,7 +282,7 @@ int alloc_shrinker_info(struct mem_cgrou > } > up_write(&shrinker_rwsem); > > - return ret; > + return 0; > } > > static inline bool need_expand(int nr_max)