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 88A60C77B7C for ; Thu, 3 Jul 2025 05:57:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1CA588E0003; Thu, 3 Jul 2025 01:57:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1754C8E0002; Thu, 3 Jul 2025 01:57:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0647A8E0003; Thu, 3 Jul 2025 01:57:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id EA4448E0002 for ; Thu, 3 Jul 2025 01:57:55 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 7F2FBBA910 for ; Thu, 3 Jul 2025 05:57:55 +0000 (UTC) X-FDA: 83621897310.18.27ABEDC Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf23.hostedemail.com (Postfix) with ESMTP id 9759A140002 for ; Thu, 3 Jul 2025 05:57:53 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=thoISwQL; spf=pass (imf23.hostedemail.com: domain of dennis@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=dennis@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1751522273; 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=gw2LJZ5q3wiWqFADwSkOp+Mj9w8Em23PCg0jSFgd270=; b=Fh0IwAkZcnhpXGruQrgJoXbHQjoUF8MWiAMxWVagOBU5BbkWIm+4sqP+NXgVXlt7/zIClE WbX+UAO0V8xDPnFA9YxdFzynWAX6zsfvKuYBMRo/h8vOiOCsMCy4z+Cha9F0ATcKCZ+7ZL w/qUTN+cPoWlc8y0YO+4nIY5OMGk8QA= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=thoISwQL; spf=pass (imf23.hostedemail.com: domain of dennis@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=dennis@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1751522273; a=rsa-sha256; cv=none; b=HtMXGm8qIdHy9sxLvRJDr/mJfaz5HcbUVVh/Muege5L4hW8a1h4t4nFpg/wKY6t6x0xDdC cigJBsgd8kxHepF3jwdqlfIPlgki/aPgJKT0J7sbXhVxUqIPJyvqUtSud9jJgFz+DlYGTZ mIORPiALOakg9uNL0+kMJexXI+xusLo= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id BB7065C4962; Thu, 3 Jul 2025 05:57:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10FAEC4CEE3; Thu, 3 Jul 2025 05:57:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1751522272; bh=x0bqtaLqnIyJug6o4pbtBOZSZUAHS5NK6xRC8csKi/I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=thoISwQLq8WNToaz9ucAbB2oDVQEbOFc3Z8DBDQGQ8jYYvTpv28IRamleWmJLjzMS elEJgND8ucwiBui6O7jgPoYQ3QNYeRT/s36JcYfsJMAIoAoSVD29ZujteqBiKAQh+5 WhMRAi5PmGqAVXCzWm01mXptST856nA1TFJqD2xkFOoRCkWm9AaNapreCT5Rtr+C+n wRXyf8ZLf1xlnhkKJQsd9blAozGYJHU1nYWtlYPicy13uu8QWshW50IgssV9PQbD6u RMrNEVgTv8928rf6O37ALQF68UdITKlI8sVRNpVSiA5pExOAkf2W14QY/SWmFUJhSf vS/kjGK1Lpb2A== Date: Wed, 2 Jul 2025 22:57:50 -0700 From: Dennis Zhou To: Jeongjun Park Cc: Shakeel Butt , tj@kernel.org, cl@gentwo.org, akpm@linux-foundation.org, vbabka@suse.cz, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock Message-ID: References: <20250702082749.141616-1-aha310510@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9759A140002 X-Stat-Signature: nuaocq6d1xo578ci3ttnkxrno96dhzi5 X-HE-Tag: 1751522273-937963 X-HE-Meta: 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 G3TvVwS7 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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: On Thu, Jul 03, 2025 at 02:19:34PM +0900, Jeongjun Park wrote: > Shakeel Butt wrote: > > > > On Wed, Jul 02, 2025 at 05:27:49PM +0900, Jeongjun Park wrote: > > > Read/Write to pcpu_nr_populated should be performed while protected > > > by pcpu_lock. However, pcpu_nr_pages() reads pcpu_nr_populated without any > > > protection, which causes a data race between read/write. > > > > > > Therefore, when reading pcpu_nr_populated in pcpu_nr_pages(), it should be > > > modified to be protected by pcpu_lock. > > > > > > Reported-by: syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com > > > Fixes: 7e8a6304d541 ("/proc/meminfo: add percpu populated pages count") > > > Signed-off-by: Jeongjun Park > > > --- > > > mm/percpu.c | 8 +++++++- > > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > > > diff --git a/mm/percpu.c b/mm/percpu.c > > > index b35494c8ede2..0f98b857fb36 100644 > > > --- a/mm/percpu.c > > > +++ b/mm/percpu.c > > > @@ -3355,7 +3355,13 @@ void __init setup_per_cpu_areas(void) > > > */ > > > unsigned long pcpu_nr_pages(void) > > > { > > > - return pcpu_nr_populated * pcpu_nr_units; > > > > No need for the lock as I think race is fine here. Use something like > > the following and add a comment. > > > > data_race(READ_ONCE(pcpu_nr_populated)) * pcpu_nr_units; > > > > This race itself is not a critical security vuln, but it is a read/write > race that actually occurs. Writing to pcpu_nr_populated is already > systematically protected through pcpu_lock, so why do you think you can > ignore the data race only when reading? > As mentioned in the other thread, the reader of this value is /proc/meminfo and reading a stale value isn't the end of the world either. Thanks, Dennis