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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C4D8BC3DA40 for ; Wed, 14 Jun 2023 09:46:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244236AbjFNJqg (ORCPT ); Wed, 14 Jun 2023 05:46:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243895AbjFNJqN (ORCPT ); Wed, 14 Jun 2023 05:46:13 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 633F1DF for ; Wed, 14 Jun 2023 02:45:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686735925; 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=UjCyqPxmCD9vxBVN8OqdZcSx2BohbRjUAgubXHv/O0A=; b=IMuzfPgHZMFTGj3cxlS3KJKBUYNnXGl5mmtFrV044yYy+sSDSngJWrUHhaaafeiyXX/987 pE5uk+xtO2uAAlp3SzkSYc61r8ktBxGdvWyhI9G6fUQ3pEEX6/q5WgEh4W6iQzs6sHPzDQ V05syYWM2nZAVKlCdtu0bIDbM1lXL1E= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-277-fxmB5WdTOdS9wVER1wEvgA-1; Wed, 14 Jun 2023 05:45:23 -0400 X-MC-Unique: fxmB5WdTOdS9wVER1wEvgA-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 69E271C0A587; Wed, 14 Jun 2023 09:45:23 +0000 (UTC) Received: from localhost (unknown [10.39.192.206]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2C820492CA6; Wed, 14 Jun 2023 09:45:23 +0000 (UTC) Date: Wed, 14 Jun 2023 10:45:22 +0100 From: "Richard W.M. Jones" To: Peter Zijlstra Cc: Aaron Thompson , linux-kernel@vger.kernel.org Subject: Re: printk.time causes rare kernel boot hangs Message-ID: <20230614094522.GA7636@redhat.com> References: <20230613134105.GA10301@redhat.com> <20230614092158.GF1639749@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230614092158.GF1639749@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 14, 2023 at 11:21:58AM +0200, Peter Zijlstra wrote: > On Tue, Jun 13, 2023 at 02:41:05PM +0100, Richard W.M. Jones wrote: > > [Being tracked in this bug which contains much more detail: > > https://gitlab.com/qemu-project/qemu/-/issues/1696 ] > > Can I please just get the detail in mail instead of having to go look at > random websites? Sure, the kernel hangs after printing: [ 0.070120] x86/cpu: User Mode Instruction Prevention (UMIP) activated [ 0.070120] Last level iTLB entries: 4KB 512, 2MB 255, 4MB 127 [ 0.070120] Last level dTLB entries: 4KB 512, 2MB 255, 4MB 127, 1GB 0 [ 0.070120] Spectre V1 : Mitigation: usercopy/swapgs barriers and __user pointer sanitization [ 0.070120] Spectre V2 : Mitigation: Retpolines [ 0.070120] Spectre V2 : Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch [ 0.070120] Spectre V2 : Spectre v2 / SpectreRSB : Filling RSB on VMEXIT [ 0.070120] Spectre V2 : Enabling Speculation Barrier for firmware calls [ 0.070120] RETBleed: Mitigation: untrained return thunk [ 0.070120] Spectre V2 : mitigation: Enabling conditional Indirect Branch Prediction Barrier [ 0.070120] Speculative Store Bypass: Mitigation: Speculative Store Bypass disabled via prctl [ 0.070120] Freeing SMP alternatives memory: 48K The next message we'd expect here would be: [ 0.070794] smpboot: CPU0: AMD Ryzen 9 3900X 12-Core Processor (family: 0x17, model: 0x71, stepping: 0x0) I believe this bug would affect baremetal too, basically any kernel compiled with CONFIG_PRINTK_TIME. However the hang is very rare. > > Recent kernels hang rarely when booted on qemu. Usually you need to > > boot 100s or 1,000s of times to see the hang, compared to 292,612 [sic] > > successful boots which I was able to do before the problematic commit. > > > > A reproducer (you'll probably need to use Fedora) is: > > Debian only shop here... in fact, I still have machines without systemd. Debian should work too actually, just run the following command until it hangs: > > $ while guestfish -a /dev/null -v run >& /tmp/log; do echo -n . ; done > > > > You will need to leave it running for probably several hours, and > > examine the /tmp/log file at the end. > > > > I tracked this down to the following commit: > > > > commit f31dcb152a3d0816e2f1deab4e64572336da197d > > Author: Aaron Thompson > > Date: Thu Apr 13 17:50:12 2023 +0000 > > > > sched/clock: Fix local_clock() before sched_clock_init() > > > > Have local_clock() return sched_clock() if sched_clock_init() has not > > yet run. sched_clock_cpu() has this check but it was not included in the > > new noinstr implementation of local_clock(). > > > > (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f31dcb152a3d0816e2f1deab4e64572336da197d) > > > > Reverting this commit fixes the problem. > > > > I don't know _why_ this commit is wrong, but can we revert it as it > > causes serious problems with libguestfs hanging randomly. > > > > Or if there's anything you want me to try out then let me know, > > because I can reproduce the problem locally quite easily. > > Well, since it's virt and all, can you attach gdb to the gdb-stub and > see where it's at? Any clue is better than no clue. I'll see if this is possible, but I didn't have much luck with gdb on qemu guests in the past. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org