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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 EB4E5C433ED for ; Wed, 31 Mar 2021 18:06:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 82D0260FE8 for ; Wed, 31 Mar 2021 18:06:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 82D0260FE8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id DC9C96B007E; Wed, 31 Mar 2021 14:06:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D78F36B0080; Wed, 31 Mar 2021 14:06:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BF29E6B0081; Wed, 31 Mar 2021 14:06:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0063.hostedemail.com [216.40.44.63]) by kanga.kvack.org (Postfix) with ESMTP id A453E6B007E for ; Wed, 31 Mar 2021 14:06:53 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 4BA61640E for ; Wed, 31 Mar 2021 18:06:53 +0000 (UTC) X-FDA: 77980950306.09.41F3603 Received: from mail-ej1-f54.google.com (mail-ej1-f54.google.com [209.85.218.54]) by imf27.hostedemail.com (Postfix) with ESMTP id 0B02B80192E7 for ; Wed, 31 Mar 2021 18:06:51 +0000 (UTC) Received: by mail-ej1-f54.google.com with SMTP id ce10so31433768ejb.6 for ; Wed, 31 Mar 2021 11:06:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=bPry98kQuEJMZSqqwWzXWqlYcpUCBUTAk2E80YAvU4I=; b=VKnLzC4GTfPXZwNUPDlTxAcEUXvAjFdJozQ2D7TCqEMVlq5xc7+uXcF1NQ3GCeN3cn J+Bke+cuLbC0DEfXIXQwgK1ZtuAi1A+X96HnuTso2Df1beu4BzBTEwn+4JCzSPXV/44I dqKQIxFxnEjIG8WsdD1VnolxLcJS54HhC1uOM3tA9N88aJbnkdDLxCwAk/yP1Ka/9KBm kYZrJBYjpOHVdnfqLr+yVlqDIAa4o3v+1bzC3RgizjL9V7ENYlAMpClVUrlY3KqDlyv0 kgQgs8PPwjLoFKN+rxLMftReKIQzC9i1xYnTMyebUrZwbpN6plKGwrhUnbjDyazc5nTN Z4fQ== 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=bPry98kQuEJMZSqqwWzXWqlYcpUCBUTAk2E80YAvU4I=; b=I7MV6AeNsGJO49LbcGNEY6Xmuc2r8CwtXDRulv4SSisxGnqpIIonOf1j/trI+rdHuh s4Oz9WKrCa17kyCqtcXx74gWO0XQuJZ7DjkoR0ztITeGuXnFKcvM4TCwIhtUmSf/gwxG 7n7j0mej7rQnCFufQVrLbzH9kSZWcQQIXc8ubpFeKOW8JNeIckfrXK+ZvvvLkl9+UZIW 5ppihfmnyLWZWjDyuA2H3kB5XiBu8QEYLQ+t++hYkaJ0uJAJC368Wq51Vaj7vc4jYkW4 spEvXooaKWxWhxJvq14R+xLoyiNKqMJxLfIKQBkIThyG+SN0gSXhVUT2Zq0MkPsyS6zM U9xg== X-Gm-Message-State: AOAM531SavYppjLvwN2cT2gBsOJU00LosRucwkcb204kjImoPx/wrH+/ Zfgt4j2qL5gHwNHnp9nK2u1Rkbqe63QktD527e4= X-Google-Smtp-Source: ABdhPJxvUcuM7+TGuYwjesKc0OeSCCK2LQ6H3RaVWsqVduH9uEGQlWgeY/WodqmAKVfqJ6Q2Pxd/moBYJl+RhrKnZxA= X-Received: by 2002:a17:906:4bce:: with SMTP id x14mr4829937ejv.383.1617214011464; Wed, 31 Mar 2021 11:06:51 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Yang Shi Date: Wed, 31 Mar 2021 11:06:39 -0700 Message-ID: Subject: Re: [PATCH mmotm] mm: vmscan: fix shrinker_rwsem in free_shrinker_info() To: Shakeel Butt Cc: Hugh Dickins , Andrew Morton , kernel test robot , 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-Server: rspam01 X-Rspamd-Queue-Id: 0B02B80192E7 X-Stat-Signature: cg6trayf8g5fukxme3i89jwsgndtbagx Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf27; identity=mailfrom; envelope-from=""; helo=mail-ej1-f54.google.com; client-ip=209.85.218.54 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617214011-210611 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, Mar 31, 2021 at 6:54 AM Shakeel Butt wrote: > > 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(). Thanks, Hugh and Shakeel. I missed the report. I think Shakeel is correct, shrinker_rwsem is not required in css_free path so Shakeel's proposal should be able to fix it. I prepared a patch: diff --git a/mm/vmscan.c b/mm/vmscan.c index 64bf07cc20f2..7348c26d4cac 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -251,7 +251,12 @@ void free_shrinker_info(struct mem_cgroup *memcg) for_each_node(nid) { pn = memcg->nodeinfo[nid]; - info = shrinker_info_protected(memcg, nid); + /* + * Don't use shrinker_info_protected() helper since + * free_shrinker_info() could be called by css_free() + * without holding shrinker_rwsem. + */ + info = rcu_dereference_protected(pn->shrinker_info, true); kvfree(info); rcu_assign_pointer(pn->shrinker_info, NULL); } > > > > > 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)