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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A564C83F1D for ; Sat, 12 Jul 2025 22:28:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BA3CF6B00D5; Sat, 12 Jul 2025 18:28:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B79F46B00D8; Sat, 12 Jul 2025 18:28:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A908B6B00DA; Sat, 12 Jul 2025 18:28:51 -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 984C06B00D5 for ; Sat, 12 Jul 2025 18:28:51 -0400 (EDT) Received: from smtpin28.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id E0B091402C8 for ; Sat, 12 Jul 2025 22:28:50 +0000 (UTC) X-FDA: 83657053620.28.7831C69 Received: from nyc.source.kernel.org (nyc.source.kernel.org [147.75.193.91]) by imf01.hostedemail.com (Postfix) with ESMTP id 6DEC640007 for ; Sat, 12 Jul 2025 22:28:49 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=bzgpewHF; dmarc=none; spf=pass (imf01.hostedemail.com: domain of akpm@linux-foundation.org designates 147.75.193.91 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1752359329; 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=X21TOB0cU4TQVqw5wGMCgnkLYJBV5or4cyyai1HBYwM=; b=OsiptNbikHUEGXwd0IPwl+V//VzeM+QjUg8+c0SDwfEEOiHDqGru/kFU1Soz20uw75+UYd ESMkZkU+wD3brQcIXl0nE75GRzlJE+BSZ7EpATipUwf6ghY5deOK2/27ZNSpyXrWuRucn0 tF0yPVBDrCzA7WMsPjetRwEQUfe7bh4= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1752359329; a=rsa-sha256; cv=none; b=V61ogoNFfi6wY8+9bzTqF4MTJg2e2R7YGrzUeFNTGpmOZpETlX+2HevYlG7ymIjAIMpMzt ZhpYPPVcEsroyg0mo2mu1zA35AVM5gSKElKwD8dx8X8IxvB3KNlR7qEOrt+cJxv2PlXfWX BQQww7kJz5+wSDE1DzbQRjuVopgY0UA= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=bzgpewHF; dmarc=none; spf=pass (imf01.hostedemail.com: domain of akpm@linux-foundation.org designates 147.75.193.91 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id 97F2FA53FE5; Sat, 12 Jul 2025 22:28:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9A321C4CEEF; Sat, 12 Jul 2025 22:28:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1752359328; bh=m0xp6n6nmm94MfPfXO6Vjh3UABToOQBQq8uWmjmtmCM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bzgpewHFuKwDVgpHCqQDhuuHImdGzW28vFRzhamMw5AkSIsA6B9RafEGxZ3PXLdmD XEIK7Ces+eZ3qe7/UrV4LVDcWavNpr/m1bvlFMiQZy0Y0p6945pgg0iTsx46uvgxxc SICqhiFy1QVaYA3d8AfXKqNGR7ESnh/LlVwY2EO4= Date: Sat, 12 Jul 2025 15:28:46 -0700 From: Andrew Morton To: Vlastimil Babka Cc: Jeongjun Park , dennis@kernel.org, tj@kernel.org, cl@gentwo.org, roman.gushchin@linux.dev, rientjes@google.com, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com Subject: Re: [PATCH v2] mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock Message-Id: <20250712152846.58adeea972a6c9caac8003d1@linux-foundation.org> In-Reply-To: References: <20250703065600.132221-1-aha310510@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6DEC640007 X-Stat-Signature: w5uau5frck1k8497snr8uojbzxdjj8fp X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1752359329-212554 X-HE-Meta: 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 g9Hw2SYU c1h16ZJByqfEp6FrfZkXwpiVJhUBnNHsVCH91ORFfUrxNvQ6NP0ua995wU9xN9hpVbqgyW4YY5q0UaOJfcS+ri77OSQaGTMJ67hNyztI6vSdA7qthXKQHheZnw+0lB7EmovWi 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 Fri, 11 Jul 2025 17:56:34 +0200 Vlastimil Babka wrote: > On 7/3/25 08:56, Jeongjun Park wrote: > > pcpu_nr_pages() reads pcpu_nr_populated without any protection, which > > causes a data race between read/write. > > > > However, since this is an intended race, we should add a data_race > > annotation instead of add a spin lock. > > > > Reported-by: syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com > > Fixes: 7e8a6304d541 ("/proc/meminfo: add percpu populated pages count") > > Suggested-by: Shakeel Butt > > Signed-off-by: Jeongjun Park > > --- > > v2: Change it as suggested by Shakeel Butt > > - Link to v1: https://lore.kernel.org/all/20250702082749.141616-1-aha310510@gmail.com/ > > --- > > mm/percpu.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/percpu.c b/mm/percpu.c > > index b35494c8ede2..782cc148b39c 100644 > > --- a/mm/percpu.c > > +++ b/mm/percpu.c > > @@ -3355,7 +3355,7 @@ void __init setup_per_cpu_areas(void) > > */ > > unsigned long pcpu_nr_pages(void) > > { > > - return pcpu_nr_populated * pcpu_nr_units; > > + return data_race(READ_ONCE(pcpu_nr_populated) * pcpu_nr_units); > > Nit: pcpu_nr_units should be excluded from the scope of data_race() as no > race can happen there. This? --- a/mm/percpu.c~mm-percpu-prevent-concurrency-problem-for-pcpu_nr_populated-read-with-spin-lock-fix +++ a/mm/percpu.c @@ -3355,7 +3355,7 @@ void __init setup_per_cpu_areas(void) */ unsigned long pcpu_nr_pages(void) { - return data_race(READ_ONCE(pcpu_nr_populated) * pcpu_nr_units); + return data_race(READ_ONCE(pcpu_nr_populated)) * pcpu_nr_units; } /* _