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Tue, 15 Sep 2020 18:56:41 +0000 Subject: Re: [PATCH bpf-next] bpf: using rcu_read_lock for bpf_sk_storage_map iterator To: Jakub Kicinski CC: , , Alexei Starovoitov , Daniel Borkmann , , Martin KaFai Lau References: <20200914184630.1048718-1-yhs@fb.com> <20200915083327.7e98cf2d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20200915104001.0182ae73@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Yonghong Song Message-ID: <837b7690-247a-083d-65f5-ea9dc48b972a@fb.com> Date: Tue, 15 Sep 2020 11:56:38 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 In-Reply-To: <20200915104001.0182ae73@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MWHPR12CA0059.namprd12.prod.outlook.com (2603:10b6:300:103::21) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21c8::1005] (2620:10d:c090:400::5:15d8) by MWHPR12CA0059.namprd12.prod.outlook.com (2603:10b6:300:103::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3391.11 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 58e42de5-ee1a-46d4-715c-08d859a914f6 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Sep 2020 18:56:41.1693 (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: /gO9ViHtbywMf40z1wYABSH4+gRI9dPnL1p4SNTL/dj+2Iw76O3W1Fb8U+aKwZ3r X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB4087 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-15_13:2020-09-15,2020-09-15 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 malwarescore=0 impostorscore=0 bulkscore=0 phishscore=0 mlxlogscore=962 lowpriorityscore=0 clxscore=1015 adultscore=0 suspectscore=0 mlxscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009150149 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 9/15/20 10:40 AM, Jakub Kicinski wrote: > On Tue, 15 Sep 2020 10:35:50 -0700 Yonghong Song wrote: >> On 9/15/20 8:33 AM, Jakub Kicinski wrote: >>> On Mon, 14 Sep 2020 11:46:30 -0700 Yonghong Song wrote: >>>> Currently, we use bucket_lock when traversing bpf_sk_storage_map >>>> elements. Since bpf_iter programs cannot use bpf_sk_storage_get() >>>> and bpf_sk_storage_delete() helpers which may also grab bucket lock, >>>> we do not have a deadlock issue which exists for hashmap when >>>> using bucket_lock ([1]). >>>> >>>> If a bucket contains a lot of sockets, during bpf_iter traversing >>>> a bucket, concurrent bpf_sk_storage_{get,delete}() may experience >>>> some undesirable delays. Using rcu_read_lock() is a reasonable >>>> compromise here. Although it may lose some precision, e.g., >>>> access stale sockets, but it will not hurt performance of other >>>> bpf programs. >>>> >>>> [1] https://lore.kernel.org/bpf/20200902235341.2001534-1-yhs@fb.com >>>> >>>> Cc: Martin KaFai Lau >>>> Signed-off-by: Yonghong Song >>> >>> Sparse is not happy about it. Could you add some annotations, perhaps? >>> >>> include/linux/rcupdate.h:686:9: warning: context imbalance in 'bpf_sk_storage_map_seq_find_next' - unexpected unlock >>> include/linux/rcupdate.h:686:9: warning: context imbalance in 'bpf_sk_storage_map_seq_stop' - unexpected unlock >> >> Okay, I will try. >> >> On my system, sparse is unhappy and core dumped.... >> >> /data/users/yhs/work/net-next/include/linux/string.h:12:38: error: too >> many errors >> /bin/sh: line 1: 2710132 Segmentation fault (core dumped) sparse >> -D__linux__ -Dlinux -D__STDC__ -Dunix >> -D__unix__ -Wbitwise -Wno-return-void -Wno-unknown-attribute >> -D__x86_64__ --arch=x86 -mlittle-endian -m64 -W >> p,-MMD,net/core/.bpf_sk_storage.o.d -nostdinc -isystem >> ... >> /data/users/yhs/work/net-next/net/core/bpf_sk_storage.c >> make[3]: *** [net/core/bpf_sk_storage.o] Error 139 >> make[3]: *** Deleting file `net/core/bpf_sk_storage.o' >> >> -bash-4.4$ rpm -qf /bin/sparse >> sparse-0.5.2-1.el7.x86_64 >> -bash-4.4$ > > I think you need to build from source, sadly :( > > https://git.kernel.org/pub/scm//devel/sparse/sparse.git Indeed, building sparse from source works. After adding some __releases(RCU) and __acquires(RCU), I now have: context imbalance in 'bpf_sk_storage_map_seq_find_next' - different lock contexts for basic block I may need to restructure code to please sparse... >