On 08/17/2017 05:05 AM, Journey Journey wrote:

Anyone reproduce this problem?

You need to read Julia's previous email on this.  I think it has the 
answers you need.

-corey

Thanks

On Wed, Aug 16, 2017 at 12:39 PM, Journey Journey
[off-list ref] wrote:

quoted

Thank you all for replying my question. The Details following:

Kernel Version: 4.4.32                from
https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.4.32.tar.xz
Rt Patch Version: 4.4.32-rt43     from
https://www.kernel.org/pub/linux/kernel/projects/rt/4.4/older/patch-4.4.32-rt43.patch.gz

Configs as attached,
(1) config.4.4.32 for non rt kernel
(2) config.4.4.32.rt for rt kernel

Testcase code as attached,
(1) softlockup-nonrt.c for non rt kernel;
(2) softlockup-rt.c for rt kernel, using raw_spinlock
(3) softlockup-rt-fifo.c for rt kernel, using sched_fifo & priority 99
(4) sample Makefile for building kernel module


Test Case 1: non rt kernel + softlockup-nonrt.c
      Picture attached  nonrt-1.png
The kernel had no response for keyboard input....
      Picture attached  nonrt-2.png
After several minutes, the kdump is triggered.

Test Case 2:  rt kernel + softlockup-rt.c
      Picture attached  rt-1.png
The kernel had no response for keyboard input....
Hangs forever ........

Test Case 3:  rt kernel + softlockup-rt-fifo.c
           Picture attached  rt-2.png
The kernel had no response for keyboard input....
Hangs forever ........

Test Case 4:  rt kernel + softlockup-rt-fifo.c + throttling
          Picture attached  rt-3.png
The kernel had no response for keyboard input....
Hangs forever ........

By the way, my test environment  is virtualbox with ubuntu.
Virtualbox Configration:
   Picture attached  Virtualbox-1.png Virtualbox-2.png  Virtualbox-3.png

crashkernel config
  crashkernel=512M

Please help me, thanks all!!


On Wed, Aug 9, 2017 at 11:35 PM, Julia Cartwright [off-list ref] wrote:

quoted

On Wed, Aug 09, 2017 at 05:05:42PM +0800, Journey Journey wrote:

quoted

Test case: https://github.com/saiyamd/softlockup_test/blob/master/softlockup_test.c

Please in the future provide more information as to what you are trying
to do, what it is you are trying, what you are seeing, and why you think
it's wrong.

Because otherwise, we're forced to reverse engineer your intent. :(

I'm _guessing_ that what you meant to say was:

    I have a testcase module that I use that attempts to trigger the
    kernels softlockup detection.  Here is a link:

       https://github.com/saiyamd/softlockup_test/blob/master/softlockup_test.c

    I'm expecting it to fire the softlockup detector and panic the system
    (I use CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC in my test rig), however,
    when I load this module on an RT system, it doesn't appear to trigger
    the softlockup detector![1]

    What could be wrong?

If that's what you meant, then the answer is:

The way that you are "hogging" the CPU, on PREEMPT_RT, doesn't prevent
the kernel from scheduling other tasks in and out (including the
watchdog thread which pets the watchdog!).

Your test case, effectively is:

     spin_lock(&lock)
     while (1)
        printk("...");
     spin_unlock(&lock)

On RT, spin-lock protected regions are preemptible.  When the watchdog
hrtimer fires and wakes up the softlockup thread, that thread preempts
the thread stuck in this region and touches the watchdog.  This prevents
the watchdog threshold from being reached.

The good news for you is that it should be entirely possible for you to
trigger the softlockup detector on RT entirely in usermode.  All you'd
need to do is disable RT throttling, and set a thread SCHED_FIFO w/ prio
99 spinning.

    Julia

1: Note: this has nothing to do with Kdump whatsoever.