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Tue, 27 Oct 2020 17:42:42 +0000 Date: Tue, 27 Oct 2020 10:42:36 -0700 From: Roman Gushchin To: Muchun Song CC: , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH 1/5] mm: memcg/slab: Fix return child memcg objcg for root memcg Message-ID: <20201027174236.GB725724@carbon.dhcp.thefacebook.com> References: <20201027080256.76497-1-songmuchun@bytedance.com> <20201027080256.76497-2-songmuchun@bytedance.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201027080256.76497-2-songmuchun@bytedance.com> X-Originating-IP: [2620:10d:c090:400::4:ba7e] X-ClientProxiedBy: MWHPR11CA0023.namprd11.prod.outlook.com (2603:10b6:301:1::33) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.dhcp.thefacebook.com (2620:10d:c090:400::4:ba7e) by MWHPR11CA0023.namprd11.prod.outlook.com (2603:10b6:301:1::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3499.19 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: d30822ad-e36c-4933-3417-08d87a9fb4e2 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Oct 2020 17:42:42.7876 (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: rkm9wphU7RHHxsRJNzXKjwpDFvftDuaRgMJSxhDhIVBRt4EWG3qdMO/BaLfTkWf3 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR15MB3651 X-OriginatorOrg: fb.com X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312,18.0.737 definitions=2020-10-27_10:2020-10-26,2020-10-27 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 mlxscore=0 malwarescore=0 lowpriorityscore=0 clxscore=1011 suspectscore=0 mlxlogscore=999 phishscore=0 priorityscore=1501 impostorscore=0 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2010270105 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 27, 2020 at 04:02:52PM +0800, Muchun Song wrote: > Consider the following memcg hierarchy. > > root > / \ > A B > > If we get the objcg of memcg A failed, the get_obj_cgroup_from_current > can return the wrong objcg for the root memcg. > > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") > Signed-off-by: Muchun Song > --- > mm/memcontrol.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) Hi Muchun, thank you for the patchset! A generic note: it's usually not a good idea to group fixes with non-fixes in one patchset if fixes are planned to be backported to stable. > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 1337775b04f3..fcbd79c5023e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2945,7 +2945,7 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p) > > __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) > { > - struct obj_cgroup *objcg = NULL; > + struct obj_cgroup *objcg; > struct mem_cgroup *memcg; > > if (memcg_kmem_bypass()) > @@ -2964,6 +2964,9 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) > } > rcu_read_unlock(); > > + if (memcg == root_mem_cgroup) > + return NULL; > + > return objcg; > } I agree, it's a bug. Good catch, thanks! I would prefer a slightly different fix though. Because we're going to change how the root memory cgroup is handled (an rfc version posted here: https://lkml.org/lkml/2020/10/21/612), it's better to not use a comparison with the root_mem_cgroup and handle the obj_cgroup_tryget() return code instead. Something like this: @@ -2973,6 +2973,7 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) objcg = rcu_dereference(memcg->objcg); if (objcg && obj_cgroup_tryget(objcg)) break; + objcg = NULL; } rcu_read_unlock(); Or a more explicit: if (obj_cgroup_tryget(objcg)) { ... } else { ... } Also, please, add: Cc: stable@vger.kernel.org Thanks! From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Gushchin Subject: Re: [PATCH 1/5] mm: memcg/slab: Fix return child memcg objcg for root memcg Date: Tue, 27 Oct 2020 10:42:36 -0700 Message-ID: <20201027174236.GB725724@carbon.dhcp.thefacebook.com> References: <20201027080256.76497-1-songmuchun@bytedance.com> <20201027080256.76497-2-songmuchun@bytedance.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=date : from : to : cc : subject : message-id : references : content-type : in-reply-to : mime-version; s=facebook; bh=HKF61jpSHkELrGyeUZ9KBZQCL+Wm+QFL2+V/mDIllu8=; b=VxGGc7C9Lx9fEkCDg9Q/5lSOHDj5noPu0z4WI0KizQ0OOl9j03sm+4R6lyfqjxcKU+CO wLVo0qqcmrEWhZv3eeCgWsWOmv17rMAza1kJOzf4LijX778fpmrdxSNBtF971j2UzIIi pMsqDrkAOCHYyMi2bLEo4qCYAZHSOTirp80= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; s=selector2-fb-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=HKF61jpSHkELrGyeUZ9KBZQCL+Wm+QFL2+V/mDIllu8=; b=Ce5ijDAj/UD3WkJSCDSdZ60kGJJ7B7wpiqrTSIeUErSZpxhZd4kGut9YKCwhhqDSkDwmZGUDXA68+Mb8vAzs1O2mHdf2OvGjB5SnJl3aJyu2dyYvFVIVyYY7wVCcEyF6UfRG8BqU20F+jAmo3+WHTopvfRmDI6SlHCPMbZawsls= Content-Disposition: inline In-Reply-To: <20201027080256.76497-2-songmuchun@bytedance.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Muchun Song Cc: hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, shakeelb@google.com, iamjoonsoo.kim@lge.com, laoar.shao@gmail.com, chris@chrisdown.name, christian.brauner@ubuntu.com, peterz@infradead.org, mingo@kernel.org, keescook@chromium.org, tglx@linutronix.de, esyr@redhat.com, surenb@google.com, areber@redhat.com, elver@google.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org On Tue, Oct 27, 2020 at 04:02:52PM +0800, Muchun Song wrote: > Consider the following memcg hierarchy. > > root > / \ > A B > > If we get the objcg of memcg A failed, the get_obj_cgroup_from_current > can return the wrong objcg for the root memcg. > > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") > Signed-off-by: Muchun Song > --- > mm/memcontrol.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) Hi Muchun, thank you for the patchset! A generic note: it's usually not a good idea to group fixes with non-fixes in one patchset if fixes are planned to be backported to stable. > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 1337775b04f3..fcbd79c5023e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2945,7 +2945,7 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p) > > __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) > { > - struct obj_cgroup *objcg = NULL; > + struct obj_cgroup *objcg; > struct mem_cgroup *memcg; > > if (memcg_kmem_bypass()) > @@ -2964,6 +2964,9 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) > } > rcu_read_unlock(); > > + if (memcg == root_mem_cgroup) > + return NULL; > + > return objcg; > } I agree, it's a bug. Good catch, thanks! I would prefer a slightly different fix though. Because we're going to change how the root memory cgroup is handled (an rfc version posted here: https://lkml.org/lkml/2020/10/21/612), it's better to not use a comparison with the root_mem_cgroup and handle the obj_cgroup_tryget() return code instead. Something like this: @@ -2973,6 +2973,7 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) objcg = rcu_dereference(memcg->objcg); if (objcg && obj_cgroup_tryget(objcg)) break; + objcg = NULL; } rcu_read_unlock(); Or a more explicit: if (obj_cgroup_tryget(objcg)) { ... } else { ... } Also, please, add: Cc: stable@vger.kernel.org Thanks!