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_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 2FBC5C04AAF for ; Thu, 16 May 2019 17:38:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0378B2082E for ; Thu, 16 May 2019 17:38:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fb.com header.i=@fb.com header.b="U/xGWQ3o" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728830AbfEPRi3 (ORCPT ); Thu, 16 May 2019 13:38:29 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:47124 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726409AbfEPRi3 (ORCPT ); Thu, 16 May 2019 13:38:29 -0400 Received: from pps.filterd (m0109331.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x4GHbZK0003099 for ; Thu, 16 May 2019 10:38:27 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : mime-version : content-type; s=facebook; bh=B2SIJpPp/mlOGynEQLUWe5A/4Aq03L0X3tl4w90B9Gw=; b=U/xGWQ3ojU2JxIog44PXNp5LPf2/Ycypw+1r8vLEJyLqAzCnHVyC3zvrKUvVZK0XoAwZ DN0Y0n3NAKzNROT8Uh7Ecr++ixHJ9xnPfvBycVuQZ4gX7kxv3Xr0Nkf9WT4+yhJtCOo+ rJF8OhLSP4zv0YuxXkQW0bS/JN7M9+GwNnU= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 2shc8br1pc-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 16 May 2019 10:38:27 -0700 Received: from mx-out.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5; Thu, 16 May 2019 10:38:25 -0700 Received: by devvm2643.prn2.facebook.com (Postfix, from userid 111017) id B087112182CE9; Thu, 16 May 2019 10:38:23 -0700 (PDT) Smtp-Origin-Hostprefix: devvm From: Roman Gushchin Smtp-Origin-Hostname: devvm2643.prn2.facebook.com To: Tejun Heo CC: Oleg Nesterov , Alex Xu , , , , Roman Gushchin Smtp-Origin-Cluster: prn2c23 Subject: [PATCH RESEND] signal: unconditionally leave the frozen state in ptrace_stop() Date: Thu, 16 May 2019 10:38:21 -0700 Message-ID: <20190516173821.1498807-1-guro@fb.com> X-Mailer: git-send-email 2.17.1 X-FB-Internal: Safe MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-16_14:,, 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=317 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905160112 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alex Xu reported a regression in strace, caused by the introduction of the cgroup v2 freezer. The regression can be reproduced by stracing the following simple program: #include int main() { write(1, "a", 1); return 0; } An attempt to run strace ./a.out leads to the infinite loop: [ pre-main omitted ] write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) [ repeats forever ] The problem occurs because the traced task leaves ptrace_stop() (and the signal handling loop) with the frozen bit set. So let's call cgroup_leave_frozen(true) unconditionally after sleeping in ptrace_stop(). With this patch applied, strace works as expected: [ pre-main omitted ] write(1, "a", 1) = 1 exit_group(0) = ? +++ exited with 0 +++ Reported-by: Alex Xu Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer") Signed-off-by: Roman Gushchin Acked-by: Oleg Nesterov Cc: Tejun Heo --- kernel/signal.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/signal.c b/kernel/signal.c index 8607b11ff936..565ba14d89d5 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2112,6 +2112,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t preempt_enable_no_resched(); cgroup_enter_frozen(); freezable_schedule(); + cgroup_leave_frozen(true); } else { /* * By the time we got the lock, our tracer went away. -- 2.20.1