Why gdb doesn't print thread stack trace for running process?

Issue

• gdb when attached to a process gives a warning.

  warning: File "/lib64/libthread_db-1.0.so" auto-loading has been declined by your `auto-load safe-path' set to "/usr/share/gdb/auto-load:/usr/lib/debug:/usr/bin/mono-gdb.py".
  
  warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.
  

• pstack doesn't print stack trace for process threads.

  # pstack 1524
  Thread 1 (process 1524):
  #0  0x00007feb8e0d12a5 in wait () from /lib64/libpthread.so.0
  #1  0x0000000000000000 in ?? ()