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=-9.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,T_DKIMWL_WL_HIGH,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 2CB6DC04A6B for ; Wed, 8 May 2019 20:34:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E37E221734 for ; Wed, 8 May 2019 20:34:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fb.com header.i=@fb.com header.b="i5gP1jg6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728175AbfEHUee (ORCPT ); Wed, 8 May 2019 16:34:34 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:55542 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726526AbfEHUed (ORCPT ); Wed, 8 May 2019 16:34:33 -0400 Received: from pps.filterd (m0148461.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x48KCiGj013909 for ; Wed, 8 May 2019 13:34:32 -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=Qt+4ylLnsNwTDXffLjsnqCa0p2J66ZSO/dTW7jmxMrs=; b=i5gP1jg6fN0KMm6q0bZqZ+iYGFQKj0c1t9mvLuNSGFkqNUhXD1/9xqDcid3Su183xR0L aT5aKwIUhe+VVOfxuoJDmj0XAwJABxHxSUhVPok4tmhvHssnapi4ZzB/z7iCZiJiOp/d I2FVUglTsKu4EHrLYKwDzgrZVZWpwgYebGg= Received: from mail.thefacebook.com (mailout.thefacebook.com [199.201.64.23]) by mx0a-00082601.pphosted.com with ESMTP id 2sc05qshuu-5 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-SHA384 bits=256 verify=NOT) for ; Wed, 08 May 2019 13:34:32 -0700 Received: from mx-out.facebook.com (2620:10d:c081:10::13) by mail.thefacebook.com (2620:10d:c081:35::125) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA) id 15.1.1713.5; Wed, 8 May 2019 13:34:31 -0700 Received: by devvm2643.prn2.facebook.com (Postfix, from userid 111017) id E81D811CDD2A0; Wed, 8 May 2019 13:34:30 -0700 (PDT) Smtp-Origin-Hostprefix: devvm From: Roman Gushchin Smtp-Origin-Hostname: devvm2643.prn2.facebook.com To: Tejun Heo CC: Oleg Nesterov , , , , Qian Cai , Roman Gushchin Smtp-Origin-Cluster: prn2c23 Subject: [PATCH] cgroup: never call do_group_exit() with task->frozen bit set Date: Wed, 8 May 2019 13:34:20 -0700 Message-ID: <20190508203420.580163-1-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=2019-05-08_11:,, signatures=0 X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I've got two independent reports that cgroup_task_frozen() check in cgroup_exit() has been triggered by lkp libhugetlbfs-test and LTP ptrace01 tests. For example: [ 44.576072] WARNING: CPU: 1 PID: 3028 at kernel/cgroup/cgroup.c:5932 cgroup_exit+0x148/0x160 [ 44.577724] Modules linked in: crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel sr_mod cdrom bochs_drm sg ttm ata_generic pata_acpi ppdev drm_kms_helper snd_pcm syscopyarea aesni_intel snd_timer sysfillrect sysimgblt snd crypto_simd cryptd glue_helper soundcore fb_sys_fops joydev drm serio_raw pcspkr ata_piix libata i2c_piix4 floppy parport_pc parport ip_tables [ 44.583106] CPU: 1 PID: 3028 Comm: ptrace-write-hu Not tainted 5.1.0-rc3-00053-g9262503 #5 [ 44.584600] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 [ 44.586116] RIP: 0010:cgroup_exit+0x148/0x160 [ 44.587135] Code: 0f 84 50 ff ff ff 48 8b 85 c8 0c 00 00 48 8b 78 70 e8 ec 2e 00 00 e9 3b ff ff ff f0 ff 43 60 0f 88 72 21 89 00 e9 48 ff ff ff <0f> 0b e9 1b ff ff ff e8 3c 73 f4 ff 66 90 66 2e 0f 1f 84 00 00 00 [ 44.590113] RSP: 0018:ffffb25702dcfd30 EFLAGS: 00010002 [ 44.591167] RAX: ffff96a7fee32410 RBX: ffff96a7ff1d6000 RCX: dead000000000200 [ 44.592446] RDX: ffff96a7ff1d6080 RSI: ffff96a7fec75290 RDI: ffff96a7fec75290 [ 44.593715] RBP: ffff96a7fec745c0 R08: ffff96a7fec74658 R09: 0000000000000000 [ 44.594985] R10: 0000000000000000 R11: 0000000000000001 R12: ffff96a7fec75101 [ 44.596266] R13: ffff96a7fec745c0 R14: ffff96a7ff3bde30 R15: ffff96a7fec75130 [ 44.597550] FS: 0000000000000000(0000) GS:ffff96a7dd700000(0000) knlGS:0000000000000000 [ 44.598950] CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 [ 44.600098] CR2: 00000000f7a00000 CR3: 000000000d20e000 CR4: 00000000000406e0 [ 44.601417] Call Trace: [ 44.602777] do_exit+0x337/0xc40 [ 44.603677] do_group_exit+0x3a/0xa0 [ 44.604610] get_signal+0x12e/0x8d0 [ 44.605533] ? __switch_to_asm+0x40/0x70 [ 44.606503] do_signal+0x36/0x650 [ 44.607409] ? __switch_to_asm+0x40/0x70 [ 44.608383] ? __schedule+0x267/0x860 [ 44.609329] exit_to_usermode_loop+0x89/0xf0 [ 44.610349] do_fast_syscall_32+0x251/0x2e3 [ 44.611357] entry_SYSENTER_compat+0x7f/0x91 [ 44.612376] ---[ end trace e4ca5cfc4b7f7964 ]--- The problem is caused by the ptrace_signal() call in the for loop in get_signal(). There is a cgroup_enter_frozen() call inside ptrace_signal(), so after exit from ptrace_signal() the task->frozen bit might be set. In this case do_group_exit() can be called with the task->frozen bit set and trigger the warning. This is only place where we can leave the loop with the task->frozen bit set and without setting JOBCTL_TRAP_FREEZE and TIF_SIGPENDING. To resolve this problem, let's move cgroup_leave_frozen(true) call to just after the fatal label. If the task is going to die, the frozen bit must be cleared no matter how we get into this point. Reported-by: kernel test robot Reported-by: Qian Cai Cc: Oleg Nesterov Cc: Tejun Heo Signed-off-by: Roman Gushchin --- kernel/signal.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 16b72f4f14df..8607b11ff936 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2483,10 +2483,6 @@ bool get_signal(struct ksignal *ksig) ksig->info.si_signo = signr = SIGKILL; sigdelset(¤t->pending.signal, SIGKILL); recalc_sigpending(); - current->jobctl &= ~JOBCTL_TRAP_FREEZE; - spin_unlock_irq(&sighand->siglock); - if (unlikely(cgroup_task_frozen(current))) - cgroup_leave_frozen(true); goto fatal; } @@ -2608,8 +2604,10 @@ bool get_signal(struct ksignal *ksig) continue; } - spin_unlock_irq(&sighand->siglock); fatal: + spin_unlock_irq(&sighand->siglock); + if (unlikely(cgroup_task_frozen(current))) + cgroup_leave_frozen(true); /* * Anything else is fatal, maybe with a core dump. -- 2.20.1