How to debug hard lockup issue

[Jassi Brar]

On 2 August 2012 15:00, Lin Ming <minggr at gmail.com> wrote:
> On Thu, Aug 2, 2012 at 4:34 PM, Uwe Kleine-König
> <u.kleine-koenig at pengutronix.de> wrote:
>> On Thu, Aug 02, 2012 at 03:59:36PM +0800, Lin Ming wrote:
>>> On Thu, Aug 2, 2012 at 3:15 PM, Uwe Kleine-König
>>> <u.kleine-koenig at pengutronix.de> wrote:
>>> > Hello,
>>> >
>>> > On Thu, Aug 02, 2012 at 11:03:31AM +0800, Lin Ming wrote:
>>> >> I encountered a hard lockup on a armv5 board with 2.6.32 kernel.
>>> >> There is no any message output since it is hard lockup.
>>> >>
>>> >> I tried watchdog, but watchdog can only reset the board. I still can't
>>> >> get any info.
>>> >>
>>> >> The hard lockup is possibly because kernel blocked/looped with
>>> >> interrupts disabled.
>>> >>
>>> >> Is there any non-maskable interrupt I can use to dump the kernel stack?
>>> >> Or any other hint?
>>> > Try enabling various debug options. The following come to (my) mind:
>>> >
>>> > CONFIG_DETECT_HUNG_TASK
>>> > CONFIG_PROVE_LOCKING
>>> > CONFIG_DEBUG_ATOMIC_SLEEP
>>> > CONFIG_MAGIC_SYSRQ
>>>
>>> These debug options are already enabled.
>>> But it doesn't help.
>> then if you don't have a hardware debugger handy you can try
>>
>>         https://lkml.org/lkml/2012/5/26/83
>
> Will try pstore and PostMortem.
>
If the hang is after bootup, pstore is a better option. If the hang is
consistent and during boot, dumping __log_buf is the only option.