From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751364AbWGLNg2 (ORCPT ); Wed, 12 Jul 2006 09:36:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751365AbWGLNg2 (ORCPT ); Wed, 12 Jul 2006 09:36:28 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:27606 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1751364AbWGLNg1 (ORCPT ); Wed, 12 Jul 2006 09:36:27 -0400 Subject: PATCH: Minimal fix for sysrq on serial console hang From: Alan Cox To: torvalds@osdl.org, linux-kernel@vger.kernel.org, rmk@arm.linux.org.uk Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 12 Jul 2006 14:54:21 +0100 Message-Id: <1152712461.22943.58.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.2 (2.6.2-1.fc5.5) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org When I originally did this change I used oops_in_progress as a locking guide. However it turns out there is one other place that turns all the locking on its head and that is sysrq. The fix below is a minimal fix to avoid this hanging and worst case may lead to the very rare stuck character as it did pre 2.6.16 anyway but only when using sysrq [which right now hangs the box] The right fix is probably to unlock on the sysrq path and relock and reconfigure the uart but thats more complex and not low risk at this point in time although I will revisit it after (or during KS/OLS) depending on rmk's view. Signed-off-by: Alan Cox diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.18-rc1/drivers/serial/8250.c linux-2.6.18-rc1/drivers/serial/8250.c --- linux.vanilla-2.6.18-rc1/drivers/serial/8250.c 2006-07-12 12:16:47.000000000 +0100 +++ linux-2.6.18-rc1/drivers/serial/8250.c 2006-07-12 12:21:10.000000000 +0100 @@ -2240,10 +2240,12 @@ touch_nmi_watchdog(); - if (oops_in_progress) { - locked = spin_trylock_irqsave(&up->port.lock, flags); - } else - spin_lock_irqsave(&up->port.lock, flags); + /* + * This can occur during an oops, in which case we want to + * do our best, or sysrq which is hairier and eventually needs + * a nicer solution + */ + locked = spin_trylock_irqsave(&up->port.lock, flags); /* * First save the IER then disable the interrupts