From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751373AbWGLNr6 (ORCPT ); Wed, 12 Jul 2006 09:47:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751372AbWGLNr5 (ORCPT ); Wed, 12 Jul 2006 09:47:57 -0400 Received: from caramon.arm.linux.org.uk ([212.18.232.186]:33041 "EHLO caramon.arm.linux.org.uk") by vger.kernel.org with ESMTP id S1751369AbWGLNr4 (ORCPT ); Wed, 12 Jul 2006 09:47:56 -0400 Date: Wed, 12 Jul 2006 14:47:49 +0100 From: Russell King To: Alan Cox Cc: torvalds@osdl.org, linux-kernel@vger.kernel.org Subject: Re: PATCH: Minimal fix for sysrq on serial console hang Message-ID: <20060712134749.GA11047@flint.arm.linux.org.uk> Mail-Followup-To: Alan Cox , torvalds@osdl.org, linux-kernel@vger.kernel.org References: <1152712461.22943.58.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1152712461.22943.58.camel@localhost.localdomain> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 12, 2006 at 02:54:21PM +0100, Alan Cox wrote: > 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. Well, akpm's had a fix in his tree for some time, which he's been pestering me with, so I committed that a few days ago: # Author: Andrew Morton (Fri Jun 30 10:29:59 BST 2006) # Committer: Russell King (Sun Jul 9 21:11:10 BST 2006) # # [SERIAL] 8250: sysrq deadlock fix # # Fix http://bugzilla.kernel.org/show_bug.cgi?id=6716 # # Doing a sysrq over a serial line into an SMP machine presently deadlocks. # # Signed-off-by: Andrew Morton # Signed-off-by: Russell King # # drivers/serial/8250.c | 13 +++++++++---- # 1 files changed, 9 insertions(+), 4 deletions(-) # diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 0995430..0ae9ced 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -2240,10 +2252,14 @@ serial8250_console_write(struct console touch_nmi_watchdog(); - if (oops_in_progress) { - locked = spin_trylock_irqsave(&up->port.lock, flags); + local_irq_save(flags); + if (up->port.sysrq) { + /* serial8250_handle_port() already took the lock */ + locked = 0; + } else if (oops_in_progress) { + locked = spin_trylock(&up->port.lock); } else - spin_lock_irqsave(&up->port.lock, flags); + spin_lock(&up->port.lock); /* * First save the IER then disable the interrupts @@ -2265,7 +2281,8 @@ serial8250_console_write(struct console serial_out(up, UART_IER, ier); if (locked) - spin_unlock_irqrestore(&up->port.lock, flags); + spin_unlock(&up->port.lock); + local_irq_restore(flags); } static int serial8250_console_setup(struct console *co, char *options) -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core