Chris Ball wrote:
> Hi,
>
> I found a machine to test my radeon patch on, but the system appears
> to hang on entering kdb, even without KMS enabled:
>
> [r...@f12 ~]# echo 9 > /proc/sys/kernel/printk
> [r...@f12 ~]# echo g > /proc/sysrq-trigger
> SysRq : DEBUG
>
> Entering kdb (current=0xf34dd640, pid 1427) on processor 0 due to Keyboard
> Entry
> [0]kdb>
>
>
Is it perhaps the case that you have a USB keyboard on this system?
Generally you would see a re-entrance failure if kdb was totally dead.
I do have patches for usb keyboards, but they are not yet ready to upstream.
Unless you boot with the args to enable the serial port for kdb, it
would definitely ignore your input on the serial port.
Simply change it to:
kgdboc=kbd,ttyS0,115200
Or if your baud rate is 9600 then:
kgdboc=kbd,ttyS0,9600
Or you could just reconfigure before you try it:
echo kbd,ttyS0 > /sys/module/kgdboc/parameters/kgdboc
echo g > /proc/sysrq-trigger
> At this point the system appears hung -- my serial port and keyboard
> input are totally ignored, and I have to power-cycle the machine.
> Any ideas on how to debug this?
>
>
Sure. We can add a printk in the device poll loop to see if kdb is
still "alive".
kernel/debug/debug_core.c
int dbg_io_get_char(void)
{
int ret = dbg_io_ops->read_char();
<--- Insert something like prink("X: %i", ret); --->
if (ret == NO_POLL_CHAR)
return -1;
if (!dbg_kdb_mode)
return ret;
if (ret == 127)
return 8;
return ret;
}
If that is generating lots of output, it simply means you don't have a
working input device, and we go from there. If we get no printk's then
we turn on nmi interruption and put an instrumentation point in the
debugger.
I do have a number of unpublished ways of debugging the debugger, and at
some point we'll start adding them as FAQ items.
Cheers,
Jason.
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