Message-ID: <41DE96DC.2090007@microgate.com>
Date: Fri, 07 Jan 2005 08:04:12 -0600
From: Paul Fulghum <paulkf@microgate.com>
User-Agent: Mozilla Thunderbird 1.0 (Windows/20041206)
MIME-Version: 1.0
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: Tim_T_Murphy@Dell.com, rmk+lkml@arm.linux.org.uk,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [BUG][2.6.8.1] serial driver hangs SMP kernel, but not the UP
 kernel
References: <4B0A1C17AA88F94289B0704CFABEF1AB0B4D32@ausx2kmps304.aus.amer.dell.com>	 <1105052674.24187.288.camel@localhost.localdomain>	 <41DDDB47.8050008@microgate.com> <1105062326.17176.313.camel@localhost.localdomain>
In-Reply-To: <1105062326.17176.313.camel@localhost.localdomain>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1156
Lines: 34

Alan Cox wrote:
> On Gwe, 2005-01-07 at 00:43, Paul Fulghum wrote:
> 
>>IIRC that guarantees a deadlock on SMP due to the
>>generic serial layer trying to grab a spinlock
>>that is already held. (Which prompted the original
>>bug report by Tim several months ago)
> 
> 
> I fixed the tty locking issues with that. If there are any left they
> should be solely in the serial generic code and I've no idea there

Yes, that is where the locking problems were.
When I last looked at it the problem call path was:

serial8250_interrupt();
    spin_lock(port->lock);
    serial8250_handle_port();
       receive_chars();
          flip.work.func(); /* if FLIP buffer full or low_latency set */
              ldisc->receive_buf(); /* N_TTY */
                  tty->driver->flush_chars();
                     uart_start();
                        spin_lock(port->lock); *BANG*

--
Paul Fulghum
Microgate Systems, Ltd

-
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/