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Fri, 26 Feb 2021 00:02:01 +0000 Date: Thu, 25 Feb 2021 16:01:57 -0800 From: Martin KaFai Lau To: Song Liu CC: , , , , , , Subject: Re: [PATCH v6 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage_[get|delete] Message-ID: <20210226000157.yoe7hbzocavn5udk@kafai-mbp.dhcp.thefacebook.com> References: <20210225234319.336131-1-songliubraving@fb.com> <20210225234319.336131-3-songliubraving@fb.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20210225234319.336131-3-songliubraving@fb.com> X-Originating-IP: [2620:10d:c090:400::5:fa88] X-ClientProxiedBy: MWHPR03CA0021.namprd03.prod.outlook.com (2603:10b6:300:117::31) To BY5PR15MB3571.namprd15.prod.outlook.com (2603:10b6:a03:1f6::32) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from kafai-mbp.dhcp.thefacebook.com (2620:10d:c090:400::5:fa88) by MWHPR03CA0021.namprd03.prod.outlook.com (2603:10b6:300:117::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3890.19 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?us-ascii?Q?8J7CGLJi5e4u8JG81xNBzEFucbzqdfnEyfvHBY8oMmh3pY80b9JyPXc81PN9?= =?us-ascii?Q?A0MKPV8/N69vo7L3mBeB6iq0tInDUOKaQALQ9nWaSv/JIgtAERz9ieZOYUl0?= =?us-ascii?Q?wgMYtBoJunNy1cZq0Pp0ZpiZOUy56tdaLaLCmJn6UzNgnclRUVEOoATrHzkD?= =?us-ascii?Q?KqCbD3ux0094FyYTrm8glQlJoCr8O36NXIcimO1whR4ceFKkRHYw75Q8j7T8?= =?us-ascii?Q?WU80L8qlHinHDjuNjn7w6i1DtFuYh2gdexwQcDYar9AVllofnxJ+4lufKxLy?= =?us-ascii?Q?nql3UoCrBUPC2s5un3vr7lenWlV9QyBWIgArNLAbC02FGRnKoOYr4sd+wB1G?= =?us-ascii?Q?Pwh5Q5pjIcTixLXZa2YiJvEcK93PpKK2rSybDr4k7Q+z9cJ+czWN67FCKzuA?= =?us-ascii?Q?ocnBtmA/14s5d6878dmqD65+5OSxtAA0kU+5OnNfeX8fvAbI3nte51rORQrE?= =?us-ascii?Q?vpB5bbmVQLNSSccYp6ViR+bjzo/9cbnPJ2ZWBPDEZitaI81BY4C2JUUdL3c8?= =?us-ascii?Q?gr4CEiuGDS8CWwRH+fmvksxy+zcV9yWdoeFqsuoCQyLx25QprcmFw9LCK0F9?= =?us-ascii?Q?PvVFFey/6v4iCjxJUliFVSZoDmiV+yl53Np312rMBu4eqhZZ61fjFCloDg7L?= =?us-ascii?Q?v11tt45tuE0xCyMJMKc3oB/IUInIlHuxI27B0d/y28PB27SI5Uc3A+XyuRkh?= =?us-ascii?Q?QjjhRfEgtfgA2bOKw5ZN0vknVQu0d3wjicSZ+nrS+03BAToZf95VSpuLtrD0?= =?us-ascii?Q?SohgTMwOlHyQsI/DQcVB2vKBMxBs+1FTBYJXjFuHMiSZzDV5zuBMuHvMvXs3?= =?us-ascii?Q?79+V7Rf5Q9tcuQ2flyqZL/i90HCzP8d6UOs9fp4GH/rWnJMUUk1MoGrUAH61?= =?us-ascii?Q?7ax1JtL/2kbyOqtiqEcLqsB4pkuod/oKszC/6FupNq4Wz1dlHu/Y92svs/0J?= =?us-ascii?Q?YL67ozRpIJSpBe8UaopMweWT0SLZ9waMYYyYD9mC+l51WQfePEgI6qNF5JJU?= =?us-ascii?Q?h5xZjeNHbvqh433gVOm+pKqxq9/bJNZSrvmwT0nsmJhjxvvFqjAN1sa+58Ck?= =?us-ascii?Q?hcXu4O+Nng4A2HPl0cJ87lBl1dCi1zhqYOXd1cun6j33fe/zgXkBBxtqcsmj?= =?us-ascii?Q?NY66y9NTRFMH1BsLC7wxKjKCydbMhHAUOAbFa76FAlvqzCG0zgRx7pb9go9J?= =?us-ascii?Q?ZuLTIRFn2i2peAnfcOuMZaxKqH6taRp+UasNiEKtdv198aj6ObonQoK9xRmU?= =?us-ascii?Q?FNR7/WPD55daUqG52Dt+fluVIaHaaA3TbrrPoLpfNck6YQpoK+kk50DVB7Is?= =?us-ascii?Q?bRhshqrQaQ9T6EilorbF8EjI70tVHQRP7DxwbZnGTvsKqB1eDZwJFidlJqEr?= =?us-ascii?Q?U/SmCvc=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 4d266738-319e-4df5-4f21-08d8d9e9bda8 X-MS-Exchange-CrossTenant-AuthSource: BY5PR15MB3571.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Feb 2021 00:02:01.2152 (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: h6tjpBu8Dt6ndbbYmJ3jrVhRz28S+LE/MJevmyJCVYYbmvEiNhaJB48XmvV3xpZY X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2646 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-02-25_15:2021-02-24,2021-02-25 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=0 spamscore=0 clxscore=1015 mlxscore=0 malwarescore=0 lowpriorityscore=0 bulkscore=0 phishscore=0 adultscore=0 priorityscore=1501 impostorscore=0 mlxlogscore=859 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2102250183 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 25, 2021 at 03:43:15PM -0800, Song Liu wrote: > BPF helpers bpf_task_storage_[get|delete] could hold two locks: > bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling > these helpers from fentry/fexit programs on functions in bpf_*_storage.c > may cause deadlock on either locks. > > Prevent such deadlock with a per cpu counter, bpf_task_storage_busy. We > need this counter to be global, because the two locks here belong to two > different objects: bpf_local_storage_map and bpf_local_storage. If we > pick one of them as the owner of the counter, it is still possible to > trigger deadlock on the other lock. For example, if bpf_local_storage_map > owns the counters, it cannot prevent deadlock on bpf_local_storage->lock > when two maps are used. Acked-by: Martin KaFai Lau