RE: Kernel 4.9.x-rt Fully Preemptible Kernel: Issue with gdb and unexpected SIGSTOP signals

["Koehrer Mathias (ETAS/ESW5)" <mathias.koehrer@etas.com>]

Hi Sebastian,

> 
> On 2017-01-24 09:15:59 [+0000], Koehrer Mathias (ETAS/ESW5) wrote:
> > The kernel version 4.1.37-rt43 is working fine, the kernel versions 4.4.39-rt50 and
> 4.8.11-rt7 show the same strange behavior as 4.9.0-rt1.
> > Something on the way between 4.1.37-rt43 and 4.4.39-rt50 seems to cause the
> trouble.
> 
> can you check if one of the earlier v4.4-RT releases (maybe start with
> -rt2 or -rt1) also shows this behaviour?
> If not, would you have a testcase?
I tested with 4.4.0-rt2.
Here this issue occurs very rarely. I ran the gdb for about 30 times, and here I got one hit.
With the other kernel versions I got the issue in 20-40% of the cases.

I will try out the other 4.4.0 releases...

I also tried to generate an easy useable test case - without success so far.
The issue occurs with our (large) application.

Some observations I have made:
- Whenever the issue occurs, at least one thread was in the system call "clone" - either called by pthread_create() 
or by system(). I got this information by calling "info thr" inside gdb.
- I removed the calls to pthread_setschedparam() to avoid running the threads in SCHED_FIFO scheduling.
Even there I got the issue. It seems not to be related to threads running in real time priority.

My tooling (Debian testing/stretch):
gdb 7.12
gcc 6.2.1

Regards

Mathias