lkml.org 
[lkml]   [2011]   [Oct]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] TTY: serial_core: Fix crash if DCD drop during suspend
On Tue, 11 Oct 2011 17:25:44 -0700
Doug Anderson <dianders@chromium.org> wrote:

> This crash was showing up 100% of the time on Tegra CPUs when an
> agetty was running on the serial port and the console was not running
> on the serial port. The reason the Tegra saw it so reliably is that
> the Tegra CPU internally ties DTR to DCD/DSR. That means when we
> dropped DTR during suspend we would get always get an immediate DCD
> drop.
>
> The specific order of operations that were running:
> * uart_suspend_port() would be called to put the uart in suspend mode
> * we'd drop DTR (ops->set_mctrl(uport, 0)).
> * the DTR drop would be looped back in the CPU to be a DCD drop.
> * the DCD drop would look to the serial driver as a hangup
> * the hangup would call uart_shutdown()
> * ... suspend / resume happens ...
> * uart_resume_port() would be called and run the code in the
> (port->flags & ASYNC_SUSPENDED) block, which would startup the port
> (and enable tx again).
> * Since the UART would be available for tx, we'd immediately get
> an interrupt, eventually calling transmit_chars()
> * The transmit_chars() function would crash. The first crash would
> be a dereference of a NULL tty member, but since the port has been
> shutdown that was just a symptom.
>
> I have proposed a patch that would fix the Tegra CPUs here (see
> https://lkml.org/lkml/2011/10/11/444 - tty/serial: Prevent drop of DCD
> on suspend for Tegra UARTs). However, even with that fix it is still
> possible for systems that have an externally visible DCD line to see a
> crash if the DCD drops at just the right time during suspend: thus
> this patch is still useful.
>
> Signed-off-by: Doug Anderson <dianders@chromium.org>

Acked-by: Alan Cox <alan@linux.intel.com>


\
 
 \ /
  Last update: 2011-10-12 14:07    [W:0.235 / U:1.392 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site