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 42331CCD1BF for ; Tue, 28 Oct 2025 16:11:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 647D180173; Tue, 28 Oct 2025 12:11:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 61FC48013F; Tue, 28 Oct 2025 12:11:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 55C8980173; Tue, 28 Oct 2025 12:11:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 473108013F for ; Tue, 28 Oct 2025 12:11:02 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 12B2712AB77 for ; Tue, 28 Oct 2025 16:11:02 +0000 (UTC) X-FDA: 84048011964.15.034579E Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) by imf06.hostedemail.com (Postfix) with ESMTP id 59909180002 for ; Tue, 28 Oct 2025 16:11:00 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=SyxgsjzA; spf=pass (imf06.hostedemail.com: domain of roman.gushchin@linux.dev designates 95.215.58.178 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1761667860; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=D4PZj+Z/AUd5TD2H5mliXY1n/lg/WeR66f3O6rTVgL0=; b=6wj34v88tqP+79YQTPSss7zQ9GaDFt/xvmalpRQfABSAl+3g07w8WlFE1V14DWuGbD/uSf Mq05MlAW/GKqKZHwJXzlPHMY5QYuLwgOsstA4icf/ed29wNNaEOQ8heOzPKXcRhXFnKe9Z H3cQcfaLza/IyXdmircMOuOPIiI0D0E= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=SyxgsjzA; spf=pass (imf06.hostedemail.com: domain of roman.gushchin@linux.dev designates 95.215.58.178 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1761667860; a=rsa-sha256; cv=none; b=mJetJcBUujQT6DUKwXAeqzX9DI6+9kzYxI3wQZMS3seYu2Cps9uRYmSHSaPx586kO29JA5 Ac28v29+OnVSMhYDfSJrxlxHf7TjqlkJ5iIbSz5CH3xulz/a99V/QZ0B30DsrKCDJbiGaf oPilYyDWNDIR3hvwCu1j8CShrkdk8vA= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761667858; 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: in-reply-to:in-reply-to:references:references; bh=D4PZj+Z/AUd5TD2H5mliXY1n/lg/WeR66f3O6rTVgL0=; b=SyxgsjzAaP3eQ9upztzSYWfJ4WsFRqyGC+WNAlDIHsVjNFkuLy+80+fxZhJbxoF71KM/Sb 2dXtGFR0Z9YliT37NCbk2o9jgMkSzntlWrQPUd9ujQ4NC2Ewk5O6GCMZUgB8sGf6/K33Ov Tv8wxDHZwyaHL5z9MiCmBhWGX4QJh9c= From: Roman Gushchin To: bot+bpf-ci@kernel.org Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, ast@kernel.org, surenb@google.com, mhocko@kernel.org, shakeel.butt@linux.dev, hannes@cmpxchg.org, andrii@kernel.org, inwardvessel@gmail.com, linux-mm@kvack.org, cgroups@vger.kernel.org, bpf@vger.kernel.org, martin.lau@kernel.org, song@kernel.org, memxor@gmail.com, tj@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, yonghong.song@linux.dev, clm@meta.com, ihor.solodrai@linux.dev Subject: Re: [PATCH v2 08/23] mm: introduce BPF kfuncs to deal with memcg pointers In-Reply-To: <2c91977fcab04be6305bf4be57e825f7e84005d16667adcdfad0585be506537c@mail.kernel.org> (bot's message of "Mon, 27 Oct 2025 23:48:21 +0000 (UTC)") References: <20251027231727.472628-9-roman.gushchin@linux.dev> <2c91977fcab04be6305bf4be57e825f7e84005d16667adcdfad0585be506537c@mail.kernel.org> Date: Tue, 28 Oct 2025 09:10:47 -0700 Message-ID: <87ldkv57nc.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 59909180002 X-Stat-Signature: ju9mermpid6b5ai5d7pnq8j49nnomenj X-Rspam-User: X-HE-Tag: 1761667860-804939 X-HE-Meta: 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 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: bot+bpf-ci@kernel.org writes: > ``` > commit ec8e2e1769704b4f69261f36e6aaf035d47c5f0f > Author: Roman Gushchin > > mm: introduce BPF kfuncs to deal with memcg pointers > > This commit introduces two new BPF kfuncs for converting css pointers > to memcg pointers with proper reference counting: bpf_get_mem_cgroup() > and bpf_put_mem_cgroup(). > >> diff --git a/mm/Makefile b/mm/Makefile >> index 051e88c69..2d8f9beb3 100644 >> --- a/mm/Makefile >> +++ b/mm/Makefile >> @@ -107,6 +107,7 @@ obj-$(CONFIG_MEMCG) += swap_cgroup.o >> endif >> ifdef CONFIG_BPF_SYSCALL >> obj-y += bpf_oom.o >> +obj-$(CONFIG_MEMCG) += bpf_memcontrol.o >> endif >> obj-$(CONFIG_CGROUP_HUGETLB) += hugetlb_cgroup.o >> obj-$(CONFIG_GUP_TEST) += gup_test.o >> diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c >> new file mode 100644 >> index 000000000..1e4609774 >> --- /dev/null >> +++ b/mm/bpf_memcontrol.c >> @@ -0,0 +1,88 @@ >> +// SPDX-License-Identifier: GPL-2.0-or-later >> +/* >> + * Memory Controller-related BPF kfuncs and auxiliary code >> + * >> + * Author: Roman Gushchin >> + */ >> + >> +#include >> +#include >> + >> +__bpf_kfunc_start_defs(); >> + >> +/** >> + * bpf_get_mem_cgroup - Get a reference to a memory cgroup >> + * @css: pointer to the css structure >> + * >> + * Returns a pointer to a mem_cgroup structure after bumping >> + * the corresponding css's reference counter. >> + * >> + * It's fine to pass a css which belongs to any cgroup controller, >> + * e.g. unified hierarchy's main css. >> + * >> + * Implements KF_ACQUIRE semantics. >> + */ >> +__bpf_kfunc struct mem_cgroup * >> +bpf_get_mem_cgroup(struct cgroup_subsys_state *css) >> +{ >> + struct mem_cgroup *memcg = NULL; >> + bool rcu_unlock = false; >> + >> + if (!root_mem_cgroup) >> + return NULL; >> + >> + if (root_mem_cgroup->css.ss != css->ss) { > ^^^^^^^ > > Can this dereference a NULL css pointer? The function checks css for > NULL at line 42 with "if (css && css_tryget(css))", which suggests css > can be NULL. If a BPF program calls this function with a NULL css, > wouldn't it crash here before reaching that check? Here css passed as an argument to bpf_get_mem_cgroup() can't be NULL, because the BPF verifier guarantees that it's a valid css pointer. However the result of rcu_dereference_raw(cgroup->subsys[ssid]) can be NULL, this is why the "if (css && css_tryget(css))" check is required down below.