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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D6663CF885C for ; Thu, 20 Nov 2025 13:32:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2CE826B0062; Thu, 20 Nov 2025 08:32:28 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2A5DC6B007B; Thu, 20 Nov 2025 08:32:28 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1E26C6B008A; Thu, 20 Nov 2025 08:32:28 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 1190F6B0062 for ; Thu, 20 Nov 2025 08:32:28 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id B2B7512BC20 for ; Thu, 20 Nov 2025 13:32:27 +0000 (UTC) X-FDA: 84131074734.03.E489E93 Received: from out-179.mta1.migadu.com (out-179.mta1.migadu.com [95.215.58.179]) by imf29.hostedemail.com (Postfix) with ESMTP id C0AAB120010 for ; Thu, 20 Nov 2025 13:32:25 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=MrvtAjUo; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf29.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.179 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1763645546; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ybURcIVrz7mysPIWzBzQOyxvKWboFgst4pbQzAb0oQs=; b=Iend45m1ZsP+RChgpDUiEyJ5SVUZnnOqfAyD2kczBxwaeNgYkAmoKfYgz5zrVGoXWdnQM4 yEAXaQSdJkVmNve1YyUnI8gUYK2ptcKjwEaCVLWm5u5K+jT0SR86T39M+o4ftZ+Bz7PagK 2rOCZN4A0UF5GfksdRh0SeNf5E/A59A= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763645546; a=rsa-sha256; cv=none; b=3UPCy2CKZSodhTkC60xoJMlWulCP7OGSVup/8kriJxoKbyYZq5jFES+iyHFrGVmA98QSuk OaV2kI8mAX15XgAuL5hf0XlMxFQvE28TrRyGcSOjF5PBPzNM2aZ5qVip9A2L7fNplwJ220 p2re5TkK9uDvsT0IqMDlCvK1u2vmg9c= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=MrvtAjUo; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf29.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.179 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev Message-ID: <6d372282-d443-4fe4-942b-998aa742eb0a@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1763645543; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ybURcIVrz7mysPIWzBzQOyxvKWboFgst4pbQzAb0oQs=; b=MrvtAjUo07c82+yzmSH3h/kWt7CxnHcNiFmUBnzEiScilBeS3UAknDBBayZG72RaQ8b49Q WsAmvYaMaleu27E7PklGE0FVra3y9mswrhSRUNrvF0HZmdUAEY8r2jRI/jkyLrgiQttdNI kc5UbGFFwApLOHJkmNaZMpZXo4OaYmY= Date: Thu, 20 Nov 2025 21:32:09 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v1 07/26] mm: memcontrol: prevent memory cgroup release in get_mem_cgroup_from_folio() To: Harry Yoo Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng References: <9eca65dec044d4352bee84511fb58960a1402ddf.1761658310.git.zhengqi.arch@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 8uofczorpcuwpsyzr73etjnopkmipief X-Rspam-User: X-Rspamd-Queue-Id: C0AAB120010 X-Rspamd-Server: rspam10 X-HE-Tag: 1763645545-201445 X-HE-Meta: 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 H7pCSrBQ ZyLozIabhv5yiXO5XwJtTCcn0Kwus5xaOwwOsYI6VUfzQZtkEpF8Ilo2dImqqp6T5cz7cDpLop6gpsru5sL8ymg3lY87NEuU6CfHBFY5iLgUCfd1C6V+L0PYWgo2wy0NWYr1O3gA6mc5xXnL1Ej9djqtw3zX+9JGXEGCHuPnp35yQNvWdLqZ1Qkfbu1ueDphvowl9R2m72aoAOQKOlnDH+1pyu01RrKCCM24IEej30/OXCM9xYvKT3qpHY/tZJvt74ArM49mMJqqFI/M0Sjl5Aoniml9O9WKJ4342iARCvgKjOV2o8KoFKThqZYjTxmERO52HbhXkYrnsDB0= 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: List-Subscribe: List-Unsubscribe: On 11/19/25 4:06 PM, Harry Yoo wrote: > On Tue, Oct 28, 2025 at 09:58:20PM +0800, Qi Zheng wrote: >> From: Muchun Song >> >> In the near future, a folio will no longer pin its corresponding >> memory cgroup. To ensure safety, it will only be appropriate to >> hold the rcu read lock or acquire a reference to the memory cgroup >> returned by folio_memcg(), thereby preventing it from being released. >> >> In the current patch, the rcu read lock is employed to safeguard >> against the release of the memory cgroup in get_mem_cgroup_from_folio(). >> >> This serves as a preparatory measure for the reparenting of the >> LRU pages. >> >> Signed-off-by: Muchun Song >> Signed-off-by: Qi Zheng >> --- > > This patch looks correct to me, so: > Reviewed-by: Harry Yoo > > with a few side question on current implementation rather than > this change... > >> mm/memcontrol.c | 11 ++++++++--- >> 1 file changed, 8 insertions(+), 3 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index d484b632c790f..1da3ad77054d3 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -973,14 +973,19 @@ struct mem_cgroup *get_mem_cgroup_from_current(void) >> */ >> struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio) >> { >> - struct mem_cgroup *memcg = folio_memcg(folio); >> + struct mem_cgroup *memcg; >> >> if (mem_cgroup_disabled()) >> return NULL; >> >> + if (!folio_memcg_charged(folio)) >> + return root_mem_cgroup; >> + >> rcu_read_lock(); >> - if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css))) > > I have no idea why we're already calling rcu_read_lock() when a folio pins > the memcg :) +1, this was introduced by https://github.com/torvalds/linux/commit/f77f0c7514789577125c1b2df145703161736359, may be some defensive programming. > >> - memcg = root_mem_cgroup; >> +retry: >> + memcg = folio_memcg(folio); >> + if (unlikely(!css_tryget(&memcg->css))) >> + goto retry; >> rcu_read_unlock(); >> return memcg; >> } >> -- >> 2.20.1 >