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 D7C97CED617 for ; Tue, 18 Nov 2025 11:32:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0DC216B0031; Tue, 18 Nov 2025 06:32:18 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 08C7F6B007B; Tue, 18 Nov 2025 06:32:18 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EBD1D6B008A; Tue, 18 Nov 2025 06:32:17 -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 D82CF6B0031 for ; Tue, 18 Nov 2025 06:32:17 -0500 (EST) Received: from smtpin07.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 0714916052F for ; Tue, 18 Nov 2025 11:32:17 +0000 (UTC) X-FDA: 84123514314.07.A287226 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) by imf07.hostedemail.com (Postfix) with ESMTP id 1547040014 for ; Tue, 18 Nov 2025 11:32:14 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="Dg6bJIB/"; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf07.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.188 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763465535; a=rsa-sha256; cv=none; b=1cc9oUidi7JmzcJqlkYgZSarIZxWtKAMAXjWXx6oWSspRE4ymE3hxp3KOGeHfcDpv/1BU4 upgn1o8wgiHwZUOCHrDjchxgaMPI0ibFYrnfD66Wx+nJfAmxoiWX+nQwLDoYAgwxURb8gk +UnsQj63jnlZIk6+eH/ArdI/IPO+zO0= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="Dg6bJIB/"; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf07.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.188 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=1763465535; 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=IHki3f3cNtOnM09ovZSWhqC7IqaJsYo0WZIJZZw+RVU=; b=WGU5hiZewXgA+P6sWkfDQn7EqGbcker6PGZrff+qWX/k0WyfFn5DgNAZRrb4VAeRxeHg87 SfhnYaF3yf+myrbmCxZrhFg92sDLER1ktQVtyyDT6e4vgkgxnh0mHMX5qkmDsf0NcmKs8W rc92x0CZb4R1b2JiJ1cdQtzQXF76x0k= Message-ID: <17ce88c0-a5d5-4315-8074-6c0a4a4e7d64@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1763465532; 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=IHki3f3cNtOnM09ovZSWhqC7IqaJsYo0WZIJZZw+RVU=; b=Dg6bJIB/vHPh4AVUVfpV8FwbbcIyFe4Xwg9nIM5+YFjnpsAyXDBARc+5rkdZn1e4fXNptU qdr+a8+t8ycFjPbfMfgPznhx+/KDzp4xgB//bQbPiiGNoxrowBo6Cz77wMcSTbdjyVcUdO l+Tw+0GrJLPlGpjHEHBe3/wqcra2+Kk= Date: Tue, 18 Nov 2025 19:31:01 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v1 06/26] mm: memcontrol: return root object cgroup for root memory cgroup 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: <5e9743f291e7ca7b8f052775e993090ed66cfa80.1761658310.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-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 1547040014 X-Stat-Signature: ic5xa1g1xpgxgkhpzr3r4ij6dycgyfft X-HE-Tag: 1763465534-431989 X-HE-Meta: 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 FHpmAYjx /t59cspSXDeZjL4DA1sMvbD2cnsX6No9eeXFDyGsPbIoj1lp5Yd8Gc1yT2egw3aHVLVqozLgIhl4Id91p3r0DAA6AahUffCQn9i9heV1AXOWs3mXvCviGSfHY008U0Tjdqn8uwgdJ6MP5NOggoEAb7qsEo2tTlmoZYbmquEYXPnfW2vu3aQIKybVBz5O7zc7XkeUjeZHQWS86LiaxIuOwEO4/ZeWCLlSJvCl+XKKBjx4htgo= 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 11/17/25 5:41 PM, Harry Yoo wrote: > On Mon, Nov 17, 2025 at 06:17:47PM +0900, Harry Yoo wrote: >> On Tue, Oct 28, 2025 at 09:58:19PM +0800, Qi Zheng wrote: >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index 2afd7f99ca101..d484b632c790f 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -2871,7 +2865,7 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order) >>> int ret = 0; >>> >>> objcg = current_obj_cgroup(); >>> - if (objcg) { >>> + if (!obj_cgroup_is_root(objcg)) { >> >> Now that we support the page and slab allocators support allocating memory >> in NMI contexts (on some archs), current_obj_cgroup() can return NULL >> if (IS_ENABLED(CONFIG_MEMCG_NMI_UNSAFE) && in_nmi()) returns true >> (then it leads to a NULL-pointer-deref bug). > > This is a real issue, but > >> But IIUC this is applied to kmem charging only (as they use this_cpu ops >> for stats update), and we don't have to apply the same restriction to >> charging LRU pages with objcg. > > actually this should be fine for now since we use get_mem_cgroup_from_mm() > and obj_cgroup_from_memcg() instead of current_obj_cgroup() when charging > LRU pages. > > But it is not immediately obvious that there are multiple ways to get > an objcg, each with different restrictions depending on what you are > going to charge :/ Perhaps some comments need to be added. :) > >> Maybe Shakeel has more insight on this. >> >> Link: https://lore.kernel.org/all/20250519063142.111219-1-shakeel.butt@linux.dev >