From patchwork Thu Dec 3 21:59:07 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jonathan Lemon X-Patchwork-Id: 337515 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0E72C4361A for ; Thu, 3 Dec 2020 21:59:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6A7C32220F for ; Thu, 3 Dec 2020 21:59:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729457AbgLCV7v convert rfc822-to-8bit (ORCPT ); Thu, 3 Dec 2020 16:59:51 -0500 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:36990 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728177AbgLCV7v (ORCPT ); Thu, 3 Dec 2020 16:59:51 -0500 Received: from pps.filterd (m0109331.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 0B3LrtMi016676 for ; Thu, 3 Dec 2020 13:59:09 -0800 Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com with ESMTP id 356ajcmjdt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 03 Dec 2020 13:59:09 -0800 Received: from intmgw003.08.frc2.facebook.com (2620:10d:c085:208::11) by mail.thefacebook.com (2620:10d:c085:21d::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Thu, 3 Dec 2020 13:59:08 -0800 Received: by devvm2494.atn0.facebook.com (Postfix, from userid 172786) id 5F4754D64717; Thu, 3 Dec 2020 13:59:07 -0800 (PST) From: Jonathan Lemon To: , , , CC: Subject: [PATCH bpf-next] bpf: increment and use correct thread iterator Date: Thu, 3 Dec 2020 13:59:07 -0800 Message-ID: <20201203215907.975053-1-jonathan.lemon@gmail.com> X-Mailer: git-send-email 2.24.1 MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312, 18.0.737 definitions=2020-12-03_12:2020-12-03,2020-12-03 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 mlxscore=0 suspectscore=0 spamscore=0 phishscore=0 adultscore=0 priorityscore=1501 impostorscore=0 mlxlogscore=661 malwarescore=0 bulkscore=0 clxscore=1034 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012030125 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Jonathan Lemon If unable to obtain the file structure for the current task, proceed to the next task number after the one returned from task_seq_get_next(), instead of the next task number from the original iterator. Use thread_group_leader() instead of comparing tgid vs pid, which might may be racy. Only obtain the task reference count at the end of the RCU section instead of repeatedly obtaining/releasing it when iterathing though a thread group. This patch fixes a recurring RCU stall seen from task_file_seq_next(). Fixes: a650da2ee52a ("bpf: Add task and task/file iterator targets") Fixes: 67b6b863e6ab ("bpf: Avoid iterating duplicated files for task_file iterator") Signed-off-by: Jonathan Lemon --- kernel/bpf/task_iter.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index 0458a40edf10..66a52fcf589a 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -33,17 +33,17 @@ static struct task_struct *task_seq_get_next(struct pid_namespace *ns, pid = find_ge_pid(*tid, ns); if (pid) { *tid = pid_nr_ns(pid, ns); - task = get_pid_task(pid, PIDTYPE_PID); + task = pid_task(pid, PIDTYPE_PID); if (!task) { ++*tid; goto retry; - } else if (skip_if_dup_files && task->tgid != task->pid && + } else if (skip_if_dup_files && !thread_group_leader(task) && task->files == task->group_leader->files) { - put_task_struct(task); task = NULL; ++*tid; goto retry; } + get_task_struct(task); } rcu_read_unlock(); @@ -164,7 +164,7 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info) curr_files = get_files_struct(curr_task); if (!curr_files) { put_task_struct(curr_task); - curr_tid = ++(info->tid); + curr_tid = curr_tid + 1; info->fd = 0; goto again; }