Hi Scott,
Thanks for the information. "sysrq_enable_flag" is custom code
introduced as part of 'y' hack implementation. I will check with the
latest kernels to make use of "sysrq" feature.
Regrads,
Sai
On Thu, May 2, 2013 at 1:24 AM, Scott Wood <scottw...@freescale.com> wrote:
> On 04/17/2013 12:04:10 AM, saikrishna gajula wrote:
>
>> HI All,
>>
>> I am new to this group. I am working on Freescale P2020
>> platform running linux 2.6.21. I am looking for debug mechanism/utility,
>> when a multi threaded application running on linux , appears to be hung (
>> running in a tight loop,deadlock) while not able to access the board
>> through serial/SSH/Telnet.
>>
>> I was looking at Magic sysrq option in linux to generate the stack,
>> register dump when the application is hung. I am able to dump the call
>> trace in normal working conditions. But i can't use echo t >
>> /proc/sysrq-trigger and debug when the application hung.
>>
>> I am using below piece of code(drivers/serial/8250.c) on P2020RDB to
>> debug
>> the application where in , in hung situation, when i press 'y' followed
>> by
>> 't' on serial console it should go to sysrq handler, and dump the call
>> trace, but it is not happening.(simply board hung)
>>
>> {
>> if(sysrq_enable_flag)
>> handle_sysrq(ch, up->port.info->tty);
>>
>> sysrq_enable_flag = 0;
>>
>> if(ch == 'y')
>> sysrq_enable_flag = 1;
>> }
>>
>> It would be helpful if you provide any hint on the issue, or any other way
>> to debug the application in hang situations.
>>
>
> There's an erratum regarding breaks in Freescale's serial port
> implementation that has been worked around in more recent kernels. 2.6.21
> is six years old. If you update to a kernel that has the workaround, or
> backport the workaround yourself to your old kernel, you should be able to
> use a break instead of hacking in a check for 'y'.
>
> Other than that, either the kernel is hung too badly to respond to serial
> input at all (in which case use JTAG to debug) or there's something wrong
> with your 'y' hack (sysrq_enable_flag doesn't even appear in current
> kernels so I can't see if this is the case without digging through old
> code).
>
> In any case, upgrade to a newer kernel -- maybe you're hitting a bug that
> has been fixed since then.
>
> -Scott
>
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