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 485CBBE5A for ; Mon, 15 Jan 2024 08:51:50 +0000 (UTC) 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="qAI+T3ta"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="svE3Jbal" Date: Mon, 15 Jan 2024 09:51:41 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1705308702; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=UuhglXcya6j0sWfWtkAYCB5SKqg5fB+6p2lnNG25ERY=; b=qAI+T3tai6voy9/fjdgsNM256TdSrF/6QR7EGAR0w5JGU3rpZWl3W/W3m5dnvou+DsPTgv lgFOmuWKRmYopEHeIQWojb1vpxxZVPwb+lrSER36Vn3oODExyC8zrJ5kFOHDP90r4o521X sJRFZMVlkaRfc+qRfPi1aCDDXAmskEohYVlg8vMzcYnVSqc3iRAMFntC8YPPNPULMd4E/K CwhnIDf3PYYF/4e8Bm4g1JwB/1aWZS1/SWMUAuge9C0xt/hNtmCkZQn5jTs1uwP/DiwIKu LrKGe4Kddp1UzkxbyGk7MFiF595fIY1nOTpa9PKKNkSnf390TZR0yqD/Wjx3+w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1705308702; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=UuhglXcya6j0sWfWtkAYCB5SKqg5fB+6p2lnNG25ERY=; b=svE3Jbal7wJLrN84xl9wXI7kUIdsh3J/Gw7Dg5oBF+Q67ORfVdpxmzGFpKXkP0p9uPBH3E USrSg4TNrm6MkEDA== From: Sebastian Andrzej Siewior To: Petr Mladek Cc: John Ogness , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Francesco Dolcini , kernel test robot Subject: Re: [PATCH printk v3 02/14] printk: Adjust mapping for 32bit seq macros Message-ID: <20240115085141.MSS4LLsR@linutronix.de> References: <20231214214201.499426-1-john.ogness@linutronix.de> <20231214214201.499426-3-john.ogness@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: On 2024-01-12 19:14:44 [+0100], Petr Mladek wrote: >=20 > That said, I am a bit nervous that a bug like this might cause > workqueue stall and panic() the kernel. > At least, this is how I read > https://lore.kernel.org/oe-lkp/202311171611.78d41dbe-oliver.sang@intel.co= m/ well, workqueue stalls and RCU as well because the CPU spins. That is a natural consequence because the CPU makes no progress (at boot). The panic _might_ be due to panic_on_error or so. There is no scheduler, nothing so one CPU is blocked and the world ends=E2= =80=A6 > It looks like it caused some loop and refcout overlow or so. > But I might be wrong. >=20 > I would like to better understand this and check if we could prevent > it somehow. Based on memory: the problem is that the sign extension bug (the fixed bug) returned the wrong or too low sequence number. So the printk code tried again to obtain a new sequence number. And got the wrong again. And this is what looped during boot.=20 I'm not sure if this sort of lockup can happen now after the bug is fixed. I can issue a NMI backtrace on all CPUs (32) without the sync (so they all can printk immediately and not one after the other) and it prints and continues=E2=80=A6 > Best Regards, > Petr Sebastian