From patchwork Thu Mar 11 19:08:35 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yang Shi X-Patchwork-Id: 12132521 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=-13.5 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 ED302C433E0 for ; Thu, 11 Mar 2021 19:09:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7B51564EC0 for ; Thu, 11 Mar 2021 19:09:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B51564EC0 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 2A9C48D02E7; Thu, 11 Mar 2021 14:09:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2592E8D02B2; Thu, 11 Mar 2021 14:09:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0AFBD8D02E7; Thu, 11 Mar 2021 14:09:07 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0128.hostedemail.com [216.40.44.128]) by kanga.kvack.org (Postfix) with ESMTP id D3C928D02B2 for ; Thu, 11 Mar 2021 14:09:07 -0500 (EST) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 813551730873 for ; Thu, 11 Mar 2021 19:09:07 +0000 (UTC) X-FDA: 77908531134.04.184134C Received: from mail-pg1-f169.google.com (mail-pg1-f169.google.com [209.85.215.169]) by imf09.hostedemail.com (Postfix) with ESMTP id B2DC86000110 for ; Thu, 11 Mar 2021 19:09:04 +0000 (UTC) Received: by mail-pg1-f169.google.com with SMTP id v14so7357552pgq.2 for ; Thu, 11 Mar 2021 11:09:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=i2D+FuQfaS2ZRj4Qwe7N96xecJSI2gtUN3o6WXvG0vk=; b=q1nH2RikMTupiiFtmscgQ+W70fe3sDorZ4fRkLKO0XRwx+fzc24172LPMv2hziIcIF Sj0Gme3WOUqsQaMT129Zo5hCy7cm+AqdnoYV2Cuh9FuQW3Y2CCm0po075aPxccdcP7MH JQtHynViMEbBUKTFxHGjdWkTdjffgcUZdS9/R5dL+UTxEWcdWqze3uwdwYU8l/dGDHKq aJVp+6mo8dpTwNLt9NTxXBqI6czJdjPZbxuZ/IW1dEL8UGxEfeQs6DOWGB9+U/ModK9y xS9MFPQFUcmim0HU0A0XnS0WKcK5jKf7wSEN3pe5Dq2HVn+Qn8xBGNHIO3XjWMEIbKDG IwiQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=i2D+FuQfaS2ZRj4Qwe7N96xecJSI2gtUN3o6WXvG0vk=; b=ayOCDDCe7cmjio5lxK2eAF2NXjIStyH62g6x5+20ZvyMU3lWNiLET32O6Nbwg7Jc+t cB2UlAj3l6yWNTO8TpOCkGIaGfXQOE/Fl0PzwybiEGeFYmEdgQ9xDiVFbrOSls27ClaB RRujCoirUJPFbIXgfjbPqRhTUjj4xVTld4ASyD9HOx24a6t0V6rc648bcLu6aPY+tbT+ EV/8OAIs+59EQw7MR69Khtp495mfCZzfHIEy6V93UWBAz3qU815bkKCNpZqgWISRI06M PvWyw/yNKxW9BMwF9XcMp7B6OZWquiq0vhDkgmGyw3PqCApWx/ZWBvV0HyYGfCoYqb5E MqJQ== X-Gm-Message-State: AOAM53384TMHkLJTw5q3v8XfF53jFtm82BgGQ/OyPmLc52Ga/dwxAf0+ AyetWc5fxaoLj8jB98BxPgY= X-Google-Smtp-Source: ABdhPJxrXzkIllUs4SsPxfmE/PuCtdbdraco1NMsd2Am1G7MNDDRxNRwRr7Wjx+o2aWZ6a4lBHN1eg== X-Received: by 2002:aa7:9431:0:b029:1f1:52fd:5444 with SMTP id y17-20020aa794310000b02901f152fd5444mr8525393pfo.47.1615489745932; Thu, 11 Mar 2021 11:09:05 -0800 (PST) Received: from localhost.localdomain (c-73-93-239-127.hsd1.ca.comcast.net. [73.93.239.127]) by smtp.gmail.com with ESMTPSA id t12sm2999111pfe.203.2021.03.11.11.09.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Mar 2021 11:09:05 -0800 (PST) From: Yang Shi To: guro@fb.com, ktkhai@virtuozzo.com, vbabka@suse.cz, shakeelb@google.com, david@fromorbit.com, hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org Cc: shy828301@gmail.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [v10 PATCH 03/13] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Date: Thu, 11 Mar 2021 11:08:35 -0800 Message-Id: <20210311190845.9708-4-shy828301@gmail.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210311190845.9708-1-shy828301@gmail.com> References: <20210311190845.9708-1-shy828301@gmail.com> MIME-Version: 1.0 X-Stat-Signature: 157ekzy47nkn753znybarjsdow34hceu X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B2DC86000110 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=mail-pg1-f169.google.com; client-ip=209.85.215.169 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615489744-329913 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: Since memcg_shrinker_map_size just can be changed under holding shrinker_rwsem exclusively, the read side can be protected by holding read lock, so it sounds superfluous to have a dedicated mutex. Kirill Tkhai suggested use write lock since: * We want the assignment to shrinker_maps is visible for shrink_slab_memcg(). * The rcu_dereference_protected() dereferrencing in shrink_slab_memcg(), but in case of we use READ lock in alloc_shrinker_maps(), the dereferrencing is not actually protected. * READ lock makes alloc_shrinker_info() racy against memory allocation fail. alloc_shrinker_info()->free_shrinker_info() may free memory right after shrink_slab_memcg() dereferenced it. You may say shrink_slab_memcg()->mem_cgroup_online() protects us from it? Yes, sure, but this is not the thing we want to remember in the future, since this spreads modularity. And a test with heavy paging workload didn't show write lock makes things worse. Acked-by: Vlastimil Babka Acked-by: Kirill Tkhai Acked-by: Roman Gushchin Reviewed-by: Shakeel Butt Signed-off-by: Yang Shi --- mm/vmscan.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 98a44fb81f8a..b08c8d9055ae 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -187,7 +187,6 @@ static DECLARE_RWSEM(shrinker_rwsem); #ifdef CONFIG_MEMCG static int memcg_shrinker_map_size; -static DEFINE_MUTEX(memcg_shrinker_map_mutex); static void free_shrinker_map_rcu(struct rcu_head *head) { @@ -201,8 +200,6 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg, struct mem_cgroup_per_node *pn; int nid; - lockdep_assert_held(&memcg_shrinker_map_mutex); - for_each_node(nid) { pn = memcg->nodeinfo[nid]; old = rcu_dereference_protected(pn->shrinker_map, true); @@ -250,7 +247,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg) if (mem_cgroup_is_root(memcg)) return 0; - mutex_lock(&memcg_shrinker_map_mutex); + down_write(&shrinker_rwsem); size = memcg_shrinker_map_size; for_each_node(nid) { map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid); @@ -261,7 +258,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg) } rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map); } - mutex_unlock(&memcg_shrinker_map_mutex); + up_write(&shrinker_rwsem); return ret; } @@ -276,9 +273,10 @@ static int expand_shrinker_maps(int new_id) if (size <= old_size) return 0; - mutex_lock(&memcg_shrinker_map_mutex); if (!root_mem_cgroup) - goto unlock; + goto out; + + lockdep_assert_held(&shrinker_rwsem); memcg = mem_cgroup_iter(NULL, NULL, NULL); do { @@ -287,13 +285,13 @@ static int expand_shrinker_maps(int new_id) ret = expand_one_shrinker_map(memcg, size, old_size); if (ret) { mem_cgroup_iter_break(NULL, memcg); - goto unlock; + goto out; } } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); -unlock: +out: if (!ret) memcg_shrinker_map_size = size; - mutex_unlock(&memcg_shrinker_map_mutex); + return ret; }