Re: preemptirq_delay_test module can trigger crash on arm64 vm

[Joel Fernandes <joel@joelfernandes.org>]

On Fri, Apr 24, 2020 at 10:01:46AM -0400, Steven Rostedt wrote:
> On Fri, 24 Apr 2020 17:26:32 +0800
> Xiao Yang <yangx.jy@cn.fujitsu.com> wrote:
> 
> > Hi Steve, Joel
> > 
> > Sorry to bother you.
> > 
> > On my slow arm64 vm, inserting and removing preemptirq_delay_test module
> > in loops triggers kernel panic sometimes.
> > 
> > Reproduce steps:
> > Do the following steps in loops(more than 10 times):
> > [root@CentOS81-aarch64 ]# modprobe preemptirq_delay_test
> > test_mode=preempt delay=500000; rmmod preemptirq_delay_test
> > 
> >
> 
> Joel,
> 
> I never did really look at that module, but doing a quick scan, I see you
> never clean up the task you start.
> 
> Which means, you can remove the module and the task still exists, and when
> it runs, it will execute code that has been freed.
> 
> The module exit should still do a kthread_stop() on it. If anything, it
> will prevent the task existing after the module is removed.

Thanks Steve for taking a look, I will submit a fix for it ASAP and send it to you
for -rc cycle. Thanks Xiao for the report.

 - Joel