Softlockup and Hardlockup sample test module

Softlockup and Hardlockup sample test module

[Ivid Suvarna]

Hi All,

Could you please provide some sample test module for causing a
Softlockup and Hardlockup in latest kernel for SMP for testing
purposes. I assume there are some Kconfigs to be enabled as well for
this.

I had tried with the module where I put a busy loop inside spinlock
but was not able to cause any lockups. Maybe this is because of SMP
which schedule the job to other CPU. "How do I make a task to run on
single CPU only?"

I only get RCU stalls sometimes instead of softlockup when I use busy
loop inside a spinlock. Is there any explanation for difference
between these stalls and softlockup.

Thanks,
IVID

Re: Softlockup and Hardlockup sample test module

[valdis.kletnieks]

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On Sun, 15 Apr 2018 13:17:27 +0530, Ivid Suvarna said:

> I had tried with the module where I put a busy loop inside spinlock
> but was not able to cause any lockups. Maybe this is because of SMP
> which schedule the job to other CPU. "How do I make a task to run on
> single CPU only?"

So you get a kernel thread that's taken a lock and will busy-loop and not free
it.  What sort of lockup do you expect will be detected from this? Would the
results be any different if you didn't take a lock before busy-looping?

For bonus points - what additional things have to happen before a livelock
happens?

And before a deadlock happens?

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Re: Softlockup and Hardlockup sample test module

[Cong Wang]

On Sun, Apr 15, 2018 at 12:47 AM, Ivid Suvarna <ivid.suvarna@gmail.com> wrote:
> Hi All,
>
> Could you please provide some sample test module for causing a
> Softlockup and Hardlockup in latest kernel for SMP for testing
> purposes. I assume there are some Kconfigs to be enabled as well for
> this.


https://github.com/torvalds/linux/blob/master/drivers/misc/lkdtm/bugs.c#L130
Is this what you need?

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Softlockup and Hardlockup sample test module

[Ivid Suvarna]

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Hi All,

Could you please provide some sample test module for causing a Softlockup
and Hardlockup in latest kernel for SMP for only testing purposes. I assume
there are some Kconfigs to be enabled as well for this.

I had tried with the module where I put a busy loop inside spinlock but was
not able to cause any lockups. Maybe this is because of SMP which schedule
the job to other CPU. "How do I make a task to run on single CPU only?"

I only get RCU stalls sometimes instead of softlockup when I use busy loop
inside a spinlock. Is there any explanation for difference between these
stalls and softlockup.

Thanks,
IVID

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