how to hard hang the kernel from userspace?

[Daniel Walker]

On 12/07/2017 07:49 AM, valdis.kletnieks at vt.edu wrote:
> On Wed, 06 Dec 2017 16:32:26 -0800, Daniel Walker said:
>
>> and it works sometimes on UP, but it doesn't work on SMP. I also tried
> Thinking about *why* that hangs a UP should explain why it doesn't work
> on SMP.
>
>> adding in "taskset" to pin multiple version of the "yes" command to each
>> cpu in the system, but that just resulted in lots of rcu warnings.
> That's.... unexpected.

May have to do with not being able to start them all instantly enough, 
something like that.

>> The goal is to make the watchdog trigger by starving out the watchdog
>> petting process. Anyone have any ideas? I'd rather not make a kernel module.
> What are you trying to achieve by doing that?
>
> Have you tried just pointing a 'kill -9' at the watchdog monitor process?  Are you using
> in-kernel watchdogd, or one in userspace?


So typically you have a process which updates the watchdog periodically 
which I call a petting process. As I said the purpose is to trigger the 
watchdog by starving the petting process (i.e. kick process) , then the 
watchdog reboots the system.


Daniel