From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 22B54374E5A for ; Tue, 29 Sep 2026 09:14:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790673270; cv=none; b=EvJUGHIrWktNxE8JzLqcpvSaBuO2zCXqHau9p7ZtGf8fXNYOVhB5QyQeRyxW+KccdROObQodmTuBayV5s7By9D8JfTZkFewlhohFc7NiHj674a2y0+sOdQDg4iMImvU1YxLUZtcxAKCxsKN2SP6/s3rRBo/3kDkBESM1qtHg/Gg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790673270; c=relaxed/simple; bh=RAdQtygi9utLehAmIo8XcZS/kleX8azM5mwQoNzQyRE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZJN8QG2mCn/OptFCmZ0PaEaKIa5Z04yvrT28Xqn1b3L95oNhMJd48ARCzi/BpuIJYRhbhm8hfM3TDouf16MKFjtSRN/qoncOhvuoGGEeXsJ0baTQ8PXxCW8CbJRHDpRi5F8dJuziJw1GrxhF4ywZs/mvi5etlpWkxkGtVZZQLXE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=vjaFOGEM; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Wh+rhv9f; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="vjaFOGEM"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Wh+rhv9f" Date: Tue, 29 Sep 2026 11:14:15 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1790673257; 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=L2oZ92swnGjPvCS2Gj6fpfutsghiOBzz7wC81WtE+IE=; b=vjaFOGEM2zTefW4fZEyHNSSNrCPSvR0IceymBrJjT97wyImrUoPS4tOF/wOt3Zolo3yBe9 Q8Wi6J7Wj3Wphs4UWaTjjhwdNARzI9NtLS/r7T/Sz3bUyF4VFrLs2o5vG8TjoRmxOuZK5E Bt+l+IgfuB0nHYRhKGrUZcV8IauEEuZ80dsGs8k2KaEMvluMHr+gjXi6Nsj7+3AlxOn90j UkGThLPzRs9wSlzoYaHaBIpmK7dbNl49gG6hcbPFrluCwvwmBIz06cCiKc6s3s8YiFKUeA 0haU18D8dRy3DyGO2jPFILcQpXDTrndD51gwhL8KsWmkPDdRqe8RO+YGpH+Y0Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1790673257; 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=L2oZ92swnGjPvCS2Gj6fpfutsghiOBzz7wC81WtE+IE=; b=Wh+rhv9fdzM2cbTATr8h7qlKEkqF2sGk0NYmIvyaXUuU0eGDOgwWHE1emF5XkN1lL/rR7s bcWQv7Y9Rw4evKDA== From: Sebastian Andrzej Siewior To: Derek Barbosa Cc: williams@redhat.com, vkuznets@redhat.com, linux-rt-users@vger.kernel.org Subject: Re: Console Hang on SMP Secondary CPU Bringup Message-ID: <20260929091415.0yfm4bPw@linutronix.de> References: <20260928140837.058IIp53@linutronix.de> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 2026-09-28 16:54:31 [-0400], Derek Barbosa wrote: > Hi Sebastian, Hi Derek, > On Mon, Sep 28, 2026 at 04:08:37PM +0200, Sebastian Andrzej Siewior wrote: > > On 2026-09-23 12:02:31 [-0400], Derek Barbosa wrote: > > > In the v6.6-rt-rebase branch in the linux-stable-rt kernel trees, building (with > > > defconfig and additional HV drivers enabled), installing, then booting a kernel > > > in a paravirtualized Virtual Machine environment (HyperV in this case) via UEFI > > > boot may result in a unrecoverable "hang" > > > > Does this also occur in v6.6-rt15? If so, can you check v7.3-rc5 and if > > it does not occur, try other RT kernels where this started happening? > > You mean the non-rebase branch, correct? I can throw that on the TODO as well. I don't care so much about rebase vs non-rebase but the old v6.6-rt15 vs current. Just to ensure that nothing slipped in while moving forward. I would assume that the rebase and non-rebase branch are equal for a fiven version. > Just recently I tested a 7.2 kernel with PREEMPT_RT (and some other Fedora > configs) and was able to reproduce the issue. I need to confirm this though, > running some more trials and collecting data. I've been a little > scatter-brained. Oh. That is good because it is not something that exists just in this old version of printk but also in the recent one. > > This HyperV is something I can't try here, can I? > > Hmm. IIRC you either need a Windows host with the functionality enabled, or > access to some sort of Azure cloud platform [0]. It is similar to other compute > providers in terms of signup, etc. I have neither. > > Does this run in qemu where you could attach gdb and check what the CPUs > > are doing? > > > > I John's email with something similar. TLDR: I don't know what other functionalities > of Hyper-V the "Azure Cloud VMs" expose, I will play around with the knobs and > fiddle with some buttons here and there... Ah, I forget that gdb and so on does not work in the other world. > > So we are not doing PREEMPT_RT? > > The issue was reproducible in both :) > > But seeing as how the code still exists in this tree, I figured this may be the > best place to report it. The logic should be widely the same but changed in a few details to what we have now in v7.3-rc1. Also the print logic is different in RT vs non-RT (due to threaded printing and not). > It hangs right at the "cpuhp up cpu1 state cpu:kick_ap" message I had inserted. > > I will play around with some of John's suggestions, and a few more ideas I had > in mind. The question is, does it hang on its own or is related to printk message it issues. > > The printk version is a bit old but still functional :) If the problem > > does not occur in a later kernel then could think about backporting that > > printk version back to v6.6 (unless there is a single obvious cause). > > It very much is! I am pretty positive that we're only seeing the bug in > this weird corner case of HyperV (Linux guest), nbcon + high loglevel. > > Thank you for the heads up. I will report back with more results + findings > soon. The bug is just pretty tedious to reproduce. okay, thanks. Sebastian