Re: [LAD] Realtime threads and security - Linux-audio-dev

18 Feb 2011

Paul Davis:
...

 On Thu, Feb 17, 2011 at 4:53 PM, Robin Gareus &lt;robin(a)gareus.org&gt; wrote:

 > Aside of that, what about locks? I've
many times been told that one mustn't do
> anything that could block in a realtime thread. What are the consequences of
> that? Could a malicious app freeze the system by blocking in a realtime thread?

 it poses no risks to anything except itself if it does that. blocking
 in an RT thread matters to the thread, not to anything else.

 to demote RT threads that are doing too much you'd need a user-space
 watchdog like das_watchdog

Actually, das_watchdog is not very useful anymore after the kernel
developers implemented a scheme to avoid a process to take over
the machine. This built-in scheme is also a watchdog, but much
more fine graided than das_watchdog. And it is also (more often
than not) useless, so one has to press the reboot button anyway.

The sad thing is that this built-in watchdog in newer kernels fools
das_watchdog into thinking that the system is operational.
(@#$@#%%!#$$!!!)

I should look into it though, it might not be impossible to
tune das_watchdog to work again.