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=-17.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 3ED6CC43381 for ; Tue, 9 Mar 2021 18:27:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A0276522E for ; Tue, 9 Mar 2021 18:27:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230516AbhCIS1Q (ORCPT ); Tue, 9 Mar 2021 13:27:16 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:35153 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230094AbhCIS1H (ORCPT ); Tue, 9 Mar 2021 13:27:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615314426; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=IdwtO+nBORLyUijXVXbOxgr/gsljMvfSaB/v2q3YioQ=; b=Ufo2URWnGgeo4TB2GCOEkgLCcNXGGjqjcc/5UWMIimxWT+YyRpCh0eWJ/rfN4n96Y8FbjU UPM7qOvE1BFWc0r5qB/IS+VTiNkulqMDiUpR4c2eCKn2Cmnjsa3po7+FAi7NGvsVMXG9Mv aNS9S+oV55GTqL1AjyECzOv61aK4Irk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-61-C5V6JJxjOpev1uX7jV7g7w-1; Tue, 09 Mar 2021 13:27:04 -0500 X-MC-Unique: C5V6JJxjOpev1uX7jV7g7w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BF18E804333; Tue, 9 Mar 2021 18:27:02 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.83]) by smtp.corp.redhat.com (Postfix) with SMTP id CC15160CCD; Tue, 9 Mar 2021 18:26:59 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 9 Mar 2021 19:27:02 +0100 (CET) Date: Tue, 9 Mar 2021 19:26:58 +0100 From: Oleg Nesterov To: Qianli Zhao Cc: christian@brauner.io, axboe@kernel.dk, ebiederm@xmission.com, tglx@linutronix.de, pcc@google.com, linux-kernel@vger.kernel.org, zhaoqianli@xiaomi.com Subject: Re: [PATCH] exit: trigger panic when init process is set to SIGNAL_GROUP_EXIT Message-ID: <20210309182657.GA1408@redhat.com> References: <1615296712-175334-1-git-send-email-zhaoqianligood@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1615296712-175334-1-git-send-email-zhaoqianligood@gmail.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/09, Qianli Zhao wrote: > > From: Qianli Zhao > > Once any init thread finds SIGNAL_GROUP_EXIT, trigger panic immediately > instead of last thread of global init has exited, and do not allow other > init threads to exit, protect task/memory state of all sub-threads for > get reliable init coredump To be honest, I don't understand the changelog. It seems that you want to uglify the kernel to simplify the debugging of buggy init? Or what? Nor can I understand the patch. I fail to understand the games with SIGNAL_UNKILLABLE and ->siglock. And iiuc with this patch the kernel will crash if init's sub-thread execs, signal_group_exit() returns T in this case. Oleg. > [ 24.705376] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00 > [ 24.705382] CPU: 4 PID: 552 Comm: init Tainted: G S O 4.14.180-perf-g4483caa8ae80-dirty #1 > [ 24.705390] kernel BUG at include/linux/pid_namespace.h:98! > > PID: 552 CPU: 4 COMMAND: "init" > PID: 1 CPU: 7 COMMAND: "init" > core4 core7 > ... sys_exit_group() > do_group_exit() > - sig->flags = SIGNAL_GROUP_EXIT > - zap_other_threads() > do_exit() > - PF_EXITING is set > ret_to_user() > do_notify_resume() > get_signal() > - signal_group_exit > - goto fatal; > do_group_exit() > do_exit() > - PF_EXITING is set > - panic("Attempted to kill init! exitcode=0x%08x\n") > exit_notify() > find_alive_thread() //no alive sub-threads > zap_pid_ns_processes()//CONFIG_PID_NS is not set > BUG() > > Signed-off-by: Qianli Zhao > --- > We got an init crash issue, but we can't get init coredump from fulldump, we also > see BUG() triggered which calling in zap_pid_ns_processes(). > > From crash dump we can get the following information: > 1. "Attempted to kill init",init process is killed. > - Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00 > 2. At the same time as init crash, a BUG() triggered in other core. > - [ 24.705390] kernel BUG at include/linux/pid_namespace.h:98! > 3. When init thread calls exit_mm, the corresponding thread task->mm will be empty, which is not conducive to extracting coredump > > To fix the issue and save complete coredump, once find init thread is set to SIGNAL_GROUP_EXIT > trigger panic immediately,and other child threads are not allowed to exit just wait for reboot > > PID: 1 TASK: ffffffc973126900 CPU: 7 COMMAND: "init" > #0 [ffffff800805ba60] perf_trace_kernel_panic_late at ffffff99ac0bcbcc > #1 [ffffff800805bac0] die at ffffff99ac08dc64 > #2 [ffffff800805bb10] bug_handler at ffffff99ac08e398 > #3 [ffffff800805bbc0] brk_handler at ffffff99ac08529c > #4 [ffffff800805bc80] do_debug_exception at ffffff99ac0814e4 > #5 [ffffff800805bdf0] el1_dbg at ffffff99ac083298 > ->Exception > /home/work/courbet-r-stable-build/kernel/msm-4.14/include/linux/pid_namespace.h: 98 > #6 [ffffff800805be20] do_exit at ffffff99ac0c22e8 > #7 [ffffff800805be80] do_group_exit at ffffff99ac0c2658 > #8 [ffffff800805beb0] sys_exit_group at ffffff99ac0c266c > #9 [ffffff800805bff0] el0_svc_naked at ffffff99ac083cf > ->SYSCALLNO: 5e (__NR_exit_group) > > PID: 552 TASK: ffffffc9613c8f00 CPU: 4 COMMAND: "init" > #0 [ffffff801455b870] __delay at ffffff99ad32cc14 > #1 [ffffff801455b8b0] __const_udelay at ffffff99ad32cd10 > #2 [ffffff801455b8c0] msm_trigger_wdog_bite at ffffff99ac5d5be0 > #3 [ffffff801455b980] do_msm_restart at ffffff99acccc3f8 > #4 [ffffff801455b9b0] machine_restart at ffffff99ac085dd0 > #5 [ffffff801455b9d0] emergency_restart at ffffff99ac0eb6dc > #6 [ffffff801455baf0] panic at ffffff99ac0bd008 > #7 [ffffff801455bb70] do_exit at ffffff99ac0c257c > /home/work/courbet-r-stable-build/kernel/msm-4.14/kernel/exit.c: 842 > #8 [ffffff801455bbd0] do_group_exit at ffffff99ac0c2644 > #9 [ffffff801455bcc0] get_signal at ffffff99ac0d1384 > #10 [ffffff801455be60] do_notify_resume at ffffff99ac08b2a8 > #11 [ffffff801455bff0] work_pending at ffffff99ac083b8c > > --- > kernel/exit.c | 29 +++++++++++++++++++++-------- > 1 file changed, 21 insertions(+), 8 deletions(-) > > diff --git a/kernel/exit.c b/kernel/exit.c > index ef2fb929..6b2da22 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -758,6 +758,27 @@ void __noreturn do_exit(long code) > validate_creds_for_do_exit(tsk); > > /* > + * Once init group is marked for death, > + * panic immediately to get a useable coredump > + */ > + if (unlikely(is_global_init(tsk) && > + signal_group_exit(tsk->signal))) { > + spin_lock_irq(&tsk->sighand->siglock); > + if (!(tsk->signal->flags & SIGNAL_UNKILLABLE)) { > + tsk->signal->flags |= SIGNAL_UNKILLABLE; > + spin_unlock_irq(&tsk->sighand->siglock); > + panic("Attempted to kill init! exitcode=0x%08x\n", > + tsk->signal->group_exit_code ?: (int)code); > + } else { > + /* init sub-thread is dying, just wait for reboot */ > + spin_unlock_irq(&tsk->sighand->siglock); > + futex_exit_recursive(tsk); > + set_current_state(TASK_UNINTERRUPTIBLE); > + schedule(); > + } > + } > + > + /* > * We're taking recursive faults here in do_exit. Safest is to just > * leave this task alone and wait for reboot. > */ > @@ -776,14 +797,6 @@ void __noreturn do_exit(long code) > acct_update_integrals(tsk); > group_dead = atomic_dec_and_test(&tsk->signal->live); > if (group_dead) { > - /* > - * If the last thread of global init has exited, panic > - * immediately to get a useable coredump. > - */ > - if (unlikely(is_global_init(tsk))) > - panic("Attempted to kill init! exitcode=0x%08x\n", > - tsk->signal->group_exit_code ?: (int)code); > - > #ifdef CONFIG_POSIX_TIMERS > hrtimer_cancel(&tsk->signal->real_timer); > exit_itimers(tsk->signal); > -- > 1.9.1 >