From mboxrd@z Thu Jan 1 00:00:00 1970 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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 A70FEC43219 for ; Fri, 26 Apr 2019 17:59:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7BB1820656 for ; Fri, 26 Apr 2019 17:59:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fb.com header.i=@fb.com header.b="qD9mwkaV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726452AbfDZR75 (ORCPT ); Fri, 26 Apr 2019 13:59:57 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:39038 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726386AbfDZR7x (ORCPT ); Fri, 26 Apr 2019 13:59:53 -0400 Received: from pps.filterd (m0109332.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x3QHxIPR015969 for ; Fri, 26 Apr 2019 10:59:52 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type; s=facebook; bh=+UMTNtxqzrE5Cg6Nx66l9gCl1GIuLMdJPrf2D2IS40w=; b=qD9mwkaVodyVgKBnuir2SAFuzqVcSGfFaaj/1HyJqtNPbxJUA2vdEtJFd4mrmo3DCpUD GKIV56DQWSiH6CO3mzTg/XWPu+iqo7I5h3DJNkVlth6iKpBviCJUjlk3pqaVOp+7tTxq Sa4sRe5ZknIc5k5hUnhHRVNbeB0rXkJm/ws= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 2s416as5pg-2 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Fri, 26 Apr 2019 10:59:52 -0700 Received: from mx-out.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5; Fri, 26 Apr 2019 10:59:51 -0700 Received: by devvm2643.prn2.facebook.com (Postfix, from userid 111017) id 604FE115F37BE; Fri, 26 Apr 2019 10:59:48 -0700 (PDT) Smtp-Origin-Hostprefix: devvm From: Roman Gushchin Smtp-Origin-Hostname: devvm2643.prn2.facebook.com To: Tejun Heo CC: Oleg Nesterov , , , , Roman Gushchin Smtp-Origin-Cluster: prn2c23 Subject: [PATCH 1/2] cgroup: prevent spurious transition into non-frozen state Date: Fri, 26 Apr 2019 10:59:44 -0700 Message-ID: <20190426175945.2559865-2-guro@fb.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190426175945.2559865-1-guro@fb.com> References: <20190426175945.2559865-1-guro@fb.com> X-FB-Internal: Safe MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-26_12:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=786 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904260123 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If freezing of a cgroup races with waking of a task from the frozen state (like waiting in vfork() or in do_signal_stop()), a spurious transition of the cgroup state can happen. The task enters cgroup_leave_frozen(true), the cgroup->nr_frozen_tasks counter decrements, and the cgroup is switched to the unfrozen state. To prevent it, let's reserve cgroup_leave_frozen(true) for terminating processes and use cgroup_leave_frozen(false) otherwise. To avoid busy-looping in the signal handling loop waiting for JOBCTL_TRAP_FREEZE set from the cgroup freezing path, let's do it explicitly in cgroup_leave_frozen(), if the task is going to stay frozen. Suggested-by: Oleg Nesterov Signed-off-by: Roman Gushchin --- kernel/cgroup/freezer.c | 16 +++++----------- kernel/signal.c | 2 +- 2 files changed, 6 insertions(+), 12 deletions(-) diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c index 3bfbb3c8baf3..c321e768f8d3 100644 --- a/kernel/cgroup/freezer.c +++ b/kernel/cgroup/freezer.c @@ -139,19 +139,13 @@ void cgroup_leave_frozen(bool always_leave) cgroup_update_frozen(cgrp); WARN_ON_ONCE(!current->frozen); current->frozen = false; + } else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) { + spin_lock(¤t->sighand->siglock); + current->jobctl |= JOBCTL_TRAP_FREEZE; + set_thread_flag(TIF_SIGPENDING); + spin_unlock(¤t->sighand->siglock); } spin_unlock_irq(&css_set_lock); - - if (unlikely(current->frozen)) { - /* - * If the task remained in the frozen state, - * make sure it won't reach userspace without - * entering the signal handling loop. - */ - spin_lock_irq(¤t->sighand->siglock); - recalc_sigpending(); - spin_unlock_irq(¤t->sighand->siglock); - } } /* diff --git a/kernel/signal.c b/kernel/signal.c index 095e0fc57b25..16b72f4f14df 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2514,7 +2514,7 @@ bool get_signal(struct ksignal *ksig) */ if (unlikely(cgroup_task_frozen(current))) { spin_unlock_irq(&sighand->siglock); - cgroup_leave_frozen(true); + cgroup_leave_frozen(false); goto relock; } -- 2.20.1