Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 13 Aug 2020 08:56:46 -0700
From:   Roman Gushchin <guro@fb.com>
To:     Johannes Weiner <hannes@cmpxchg.org>
CC:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PowerPC Mailing List <linuxppc-dev@lists.ozlabs.org>
Subject: Re: linux-next: runtime warning in Linus' tree
Message-ID: <20200813153856.GA1641111@carbon.lan>
References: <20200813164654.061dbbd3@canb.auug.org.au>
 <20200813152033.GA701678@cmpxchg.org>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200813152033.GA701678@cmpxchg.org>
MIME-Version: 1.0
X-MS-Exchange-MessageSentRepresentingType: 1
Received: from carbon.lan (2620:10d:c090:400::5:c40b) by BY5PR16CA0021.namprd16.prod.outlook.com (2603:10b6:a03:1a0::34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3283.16 via Frontend Transport; Thu, 13 Aug 2020 15:56:48 +0000
X-Originating-IP: [2620:10d:c090:400::5:c40b]
X-MS-PublicTrafficType: Email
X-MS-Office365-Filtering-Correlation-Id: 1da9ab32-668f-4b18-1a97-08d83fa17cde
X-MS-TrafficTypeDiagnostic: BYAPR15MB2630:
X-Microsoft-Antispam-PRVS: <BYAPR15MB26301BCB38E276424318FA98BE430@BYAPR15MB2630.namprd15.prod.outlook.com>
X-FB-Source: Internal
X-MS-Oob-TLC-OOBClassifiers: OLM:2803;
X-MS-Exchange-SenderADCheck: 1
X-Microsoft-Antispam: BCL:0;
X-Microsoft-Antispam-Message-Info: YhPDGJwGv172HsB80kwiJ20iv7ardIN4G7G4Pt+kJi6lovUKfBSXlRskz7GXicPPJOPAvPxZud7pyKe2Z3DeQZDupwbe5K4E8MdcN9fdYawAjziNBBTEejSxL7moz8UZTFT0dacD0OSrUSrXOpTnEU9izkBmNko4XGTfxq24s4kfGniDtn5dIFUlpndBT8Fi35lmdwaLTOR8X9CcOa/Rlt+mP/aVzKmZblRCDVHBNK7ibZSZfbMpjsIC8XEq4GPdfjRA+8Wl/n2coK7LVwVY8UYUHuGvHxES2V06qjVE1pI9JV63djJmiS+RT/BIAc+YxAVueI7k3piSQN2onhVudA==
X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR15MB4136.namprd15.prod.outlook.com;PTR:;CAT:NONE;SFS:(136003)(376002)(366004)(396003)(39860400002)(346002)(8886007)(1076003)(66476007)(66556008)(478600001)(66946007)(2906002)(33656002)(4326008)(8676002)(55016002)(5660300002)(9686003)(54906003)(86362001)(53546011)(16526019)(6916009)(316002)(83380400001)(36756003)(6506007)(52116002)(8936002)(7696005)(186003);DIR:OUT;SFP:1102;
X-MS-Exchange-AntiSpam-MessageData: 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
X-MS-Exchange-CrossTenant-Network-Message-Id: 1da9ab32-668f-4b18-1a97-08d83fa17cde
X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Aug 2020 15:56:49.2908
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: SFMHRVInJ/SjrLansjjd6ora1H2abGC7jVy3lvQPGAI8Flwns3aOKMlG8RQ0+9mU
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2630
X-OriginatorOrg: fb.com
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687
 definitions=2020-08-13_14:2020-08-13,2020-08-13 signatures=0
X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 spamscore=0
 phishscore=0 suspectscore=1 mlxlogscore=999 priorityscore=1501
 adultscore=0 malwarescore=0 clxscore=1011 lowpriorityscore=0
 impostorscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx
 scancount=1 engine=8.12.0-2006250000 definitions=main-2008130117
X-FB-Internal: deliver
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Aug 13, 2020 at 11:20:33AM -0400, Johannes Weiner wrote:
> On Thu, Aug 13, 2020 at 04:46:54PM +1000, Stephen Rothwell wrote:
> > [    0.055220][    T0] WARNING: CPU: 0 PID: 0 at mm/memcontrol.c:5220 mem_cgroup_css_alloc+0x350/0x904
> 
> > [The line numbers in the final linux next are 5226 and 5141 due to
> > later patches.]
> > 
> > Introduced (or exposed) by commit
> > 
> >   3e38e0aaca9e ("mm: memcg: charge memcg percpu memory to the parent cgroup")
> > 
> > This commit actually adds the WARN_ON, so it either adds the bug that
> > sets it off, or the bug already existed.
> > 
> > Unfotunately, the version of this patch in linux-next up tuntil today
> > is different.  :-(
> 
> Sorry, I made a last-minute request to include these checks in that
> patch to make the code a bit more robust, but they trigger a false
> positive here. Let's remove them.
> 
> ---
> 
> From de8ea7c96c056c3cbe7b93995029986a158fb9cd Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes@cmpxchg.org>
> Date: Thu, 13 Aug 2020 10:40:54 -0400
> Subject: [PATCH] mm: memcontrol: fix warning when allocating the root cgroup
> 
> Commit 3e38e0aaca9e ("mm: memcg: charge memcg percpu memory to the
> parent cgroup") adds memory tracking to the memcg kernel structures
> themselves to make cgroups liable for the memory they are consuming
> through the allocation of child groups (which can be significant).
> 
> This code is a bit awkward as it's spread out through several
> functions: The outermost function does memalloc_use_memcg(parent) to
> set up current->active_memcg, which designates which cgroup to charge,
> and the inner functions pass GFP_ACCOUNT to request charging for
> specific allocations. To make sure this dependency is satisfied at all
> times - to make sure we don't randomly charge whoever is calling the
> functions - the inner functions warn on !current->active_memcg.
> 
> However, this triggers a false warning when the root memcg itself is
> allocated. No parent exists in this case, and so current->active_memcg
> is rightfully NULL. It's a false positive, not indicative of a bug.
> 
> Delete the warnings for now, we can revisit this later.
> 
> Fixes: 3e38e0aaca9e ("mm: memcg: charge memcg percpu memory to the parent cgroup")
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!


> ---
>  mm/memcontrol.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d59fd9af6e63..9d87082e64aa 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5137,9 +5137,6 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
>  	if (!pn)
>  		return 1;
>  
> -	/* We charge the parent cgroup, never the current task */
> -	WARN_ON_ONCE(!current->active_memcg);
> -
>  	pn->lruvec_stat_local = alloc_percpu_gfp(struct lruvec_stat,
>  						 GFP_KERNEL_ACCOUNT);
>  	if (!pn->lruvec_stat_local) {
> @@ -5222,9 +5219,6 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
>  		goto fail;
>  	}
>  
> -	/* We charge the parent cgroup, never the current task */
> -	WARN_ON_ONCE(!current->active_memcg);
> -
>  	memcg->vmstats_local = alloc_percpu_gfp(struct memcg_vmstats_percpu,
>  						GFP_KERNEL_ACCOUNT);
>  	if (!memcg->vmstats_local)
> -- 
> 2.28.0
>