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Tue, 23 Jun 2020 21:24:55 +0000 Date: Tue, 23 Jun 2020 14:24:52 -0700 From: Martin KaFai Lau To: Jakub Sitnicki CC: , , , Andrii Nakryiko Subject: Re: [PATCH bpf-next v2 2/3] bpf, netns: Keep attached programs in bpf_prog_array Message-ID: <20200623212452.titgpyrxx56u3lyd@kafai-mbp.dhcp.thefacebook.com> References: <20200623103459.697774-1-jakub@cloudflare.com> <20200623103459.697774-3-jakub@cloudflare.com> <20200623193352.4mdmfg4mfmgfeku4@kafai-mbp.dhcp.thefacebook.com> <87sgelmrba.fsf@cloudflare.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sgelmrba.fsf@cloudflare.com> User-Agent: NeoMutt/20180716 X-ClientProxiedBy: BYAPR08CA0012.namprd08.prod.outlook.com (2603:10b6:a03:100::25) To DM6PR15MB3580.namprd15.prod.outlook.com (2603:10b6:5:1f9::10) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from kafai-mbp.dhcp.thefacebook.com (2620:10d:c090:400::5:ddf5) by BYAPR08CA0012.namprd08.prod.outlook.com (2603:10b6:a03:100::25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3109.22 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 236bece9-21fc-416e-17ad-08d817bbdf64 X-MS-Exchange-CrossTenant-AuthSource: DM6PR15MB3580.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Jun 2020 21:24:55.0035 (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: yXCZx5swXW3nxA21/zcHETEDS1jOZQtylwewKOBrK9uWxNHRYW90wqi8p55E85pW X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR15MB2635 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-23_13:2020-06-23,2020-06-23 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 clxscore=1015 impostorscore=0 suspectscore=0 phishscore=0 mlxlogscore=737 priorityscore=1501 mlxscore=0 lowpriorityscore=0 adultscore=0 spamscore=0 malwarescore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006120000 definitions=main-2006230144 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Jun 23, 2020 at 10:59:37PM +0200, Jakub Sitnicki wrote: > On Tue, Jun 23, 2020 at 09:33 PM CEST, Martin KaFai Lau wrote: > > On Tue, Jun 23, 2020 at 12:34:58PM +0200, Jakub Sitnicki wrote: > > > > [ ... ] > > > >> @@ -93,8 +108,16 @@ static int bpf_netns_link_update_prog(struct bpf_link *link, > >> goto out_unlock; > >> } > >> > >> + run_array = rcu_dereference_protected(net->bpf.run_array[type], > >> + lockdep_is_held(&netns_bpf_mutex)); > >> + if (run_array) > >> + ret = bpf_prog_array_replace_item(run_array, link->prog, new_prog); > >> + else > > When will this happen? > > This will never happen, unless there is a bug. As long as there is a > link attached, run_array should never be detached (null). Because it can > be handled gracefully, we fail the bpf(LINK_UPDATE) syscall. > > Your question makes me think that perhaps it should trigger a warning, > with WARN_ON_ONCE, to signal clearly to the reader that this is an > unexpected state. > > WDYT? Thanks for confirming and the explanation. If it will never happen, I would skip the "if (run_array)". That will help the code reading in the future. I would not WARN also.