Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 8 Mar 2001 18:33:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 8 Mar 2001 18:33:42 -0500 Received: from horus.its.uow.edu.au ([130.130.68.25]:28042 "EHLO horus.its.uow.edu.au") by vger.kernel.org with ESMTP id ; Thu, 8 Mar 2001 18:33:34 -0500 Message-ID: <3AA8169F.FAE81841@uow.edu.au> Date: Thu, 08 Mar 2001 23:32:47 +0000 From: Andrew Morton X-Mailer: Mozilla 4.61 [en] (X11; I; Linux 2.4.1-pre10 i686) X-Accept-Language: en MIME-Version: 1.0 To: Andreas Dilger CC: Vibol Hou , Linux-Kernel Subject: Re: kernel BUG doing sysrq-t on 2.4.2-ac14 In-Reply-To: <200103081934.f28JYGS05891@webber.adilger.net> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andreas Dilger wrote: > > > [< c0109557>] kernel BUG at printk.c:327! > > It may be that if the tasklist is too long, and it runs with interrupts > disabled, that this will trigger the NMI watchdog timer. Since I don't > know anything about the console, I can't help. Yes, this is being a pest. I assume what is happening is that a CPU is (slowly) doing a print to the serial console with console_sem held. Then the NMI watchdog fires and it reinitialises the console semaphore. On return from the NMI handler, console_sem is now released. It's off-by-one. So subsequent attempts to use printk() hit the BUG(). ho-hum. The machine is of course completely kaput by this stage but this really should be fixed. This'll be fun to test. A wider question is why are we still getting NMI watchdog triggering during SYSRQ-T on a serial console. This is the second time this has been reported. It can certainly happen if the serial port is set up for hardware handshaking and the modem control lines aren't set up right - we loop for ever in the serial console code. Fair enough. Maybe the sysrq handler should communicate with the NMI watchdog code, and tell it not to fire while it's dumping stuff. hmm... Messy. - - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/