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
<journeywang123@xxxxxxxxx> wrote:
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 <julia@xxxxxx> wrote:
On Wed, Aug 09, 2017 at 05:05:42PM +0800, Journey Journey wrote:
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.
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