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 E3CF7C54798 for ; Sat, 9 Mar 2024 11:24:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4B13D6B0074; Sat, 9 Mar 2024 06:24:57 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 460266B0075; Sat, 9 Mar 2024 06:24:57 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 327986B0078; Sat, 9 Mar 2024 06:24:57 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 2328D6B0074 for ; Sat, 9 Mar 2024 06:24:57 -0500 (EST) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id E960F1A08EA for ; Sat, 9 Mar 2024 11:24:56 +0000 (UTC) X-FDA: 81877268592.08.9626EEE Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) by imf08.hostedemail.com (Postfix) with ESMTP id F253516000E for ; Sat, 9 Mar 2024 11:24:54 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=P8HBvKE8; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf08.hostedemail.com: domain of chengming.zhou@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=chengming.zhou@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1709983495; 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=eL7mM7sZYIm+/FYyJAxbcAh676RdIHz8wgb5OtaQOqQ=; b=xY9fTQHoKf21L95aWrW7OHxKBrfLv7CUuc6oHTOqmjSQYSV7T9A1PHpPjp6BO2WqhhfQAW fZv+BMkN+otZmOHMDpwH9ReJk6ZAbtSXKjQUNvDHKD6GrPcXvlhGV5BIzdFvyZOvKanDEU gc/LpoxqOIQkLZooxiaqE2hJX1iMPnk= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=P8HBvKE8; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf08.hostedemail.com: domain of chengming.zhou@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=chengming.zhou@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1709983495; a=rsa-sha256; cv=none; b=h63RQvn5KBUktPLN7SwwkZ8p+jAnoV8OzroIFxG/8HLQcz3CIvYWIP/0XZPVgmsLlJug2v ZsGYX+yt8X1iWt4fNn5oicoVRctAeQWw8zn2+51mDoRcMiMy7I0vGHPxsdX9qFC0pD+zNc 2sXBy8U82BRH9Ni8r/ea4pNO/iNDhbE= Message-ID: <8bc1aebf-8395-416f-8c23-53cbd25d0eef@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1709983492; 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=eL7mM7sZYIm+/FYyJAxbcAh676RdIHz8wgb5OtaQOqQ=; b=P8HBvKE8AWR+nWpWUoVPjwvk3yc6jQPFvPcr7KtVMESfTR55wM1FSzLKpvQ8P+Kj4NCPPV ZeHlzKjWzvHSMuZHuHoYKKUykgys45sWKm+xuGAM9NBbqHnUXHQaaENnc9Ga7XRPOEsAZ8 aFxe15F4yQ3UMPDxHFKIOrsBBMWvMKI= Date: Sat, 9 Mar 2024 19:24:11 +0800 MIME-Version: 1.0 Subject: Re: [PATCH] mm/slub: mark racy accesses on slab->slabs Content-Language: en-US To: linke li Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: F253516000E X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 7t9z9okj53axjhut6y8zhfca5nxs55wk X-HE-Tag: 1709983494-707926 X-HE-Meta: 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 2G3h36oI ksxgppOby4LOlI4tvk7lwEb5hJQ3PgMOPbnaXzB7xaCMpu+1UPVfX0vtfgrgABSNK402oB58NcFLAS3cnSAqRClnXJm66bIr1XD5iLf2+7DZWBJ+CE+fd0rJsmuubxZqj5QEpmTYFrEPYbiDQcfyhKhl5DJf1kylGXn7NwQzT9PDppGKd+B482gtfjA== 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 2024/3/9 15:48, linke li wrote: > The reads of slab->slabs are racy because it may be changed by > put_cpu_partial concurrently. And in slabs_cpu_partial_show ->slabs is > only used for output. Data-racy reads from shared variables that are used > only for diagnostic purposes should typically use data_race(), since it > is normally not a problem if the values are off by a little. > > This patch is aimed at reducing the number of benign races reported by > KCSAN in order to focus future debugging effort on harmful races. > > Signed-off-by: linke li > --- > mm/slub.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 2ef88bbf56a3..7b20591e7f8a 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -6257,7 +6257,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf) > slab = slub_percpu_partial(per_cpu_ptr(s->cpu_slab, cpu)); > > if (slab) > - slabs += slab->slabs; > + slabs += data_race(slab->slabs); > } > #endif > > @@ -6271,7 +6271,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf) > > slab = slub_percpu_partial(per_cpu_ptr(s->cpu_slab, cpu)); > if (slab) { > - slabs = READ_ONCE(slab->slabs); > + slabs = data_race(slab->slabs); > objects = (slabs * oo_objects(s->oo)) / 2; > len += sysfs_emit_at(buf, len, " C%d=%d(%d)", > cpu, objects, slabs); There is another unmarked access of "slab->slabs" in the show_slab_objects(), which you can change too. I'm not sure that it's really safe to access "slab->slabs" here without any protection? Although it should be no problem in practice, alternative choice maybe putting partial slabs count in the kmem_cache_cpu struct. Thanks.