Why am I unable to attach `strace` to a kworker process?

Question

As root, I try to attach strace to a running kworker process, without success.

      root@rasal# whoami
            root
      root@rasal:/# cat  /proc/sys/kernel/yama/ptrace_scope
            0
      root@rasal:/# ps ax | grep kworker
            1030 ?        S<     0:00 [kworker/u17:0]
      root@rasal:/# strace -fp 1030
            strace: attach: ptrace(PTRACE_ATTACH, ...): Operation not permitted
            Could not attach to process.  If your uid matches the uid of the target
            process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try
            again as the root user.  For more details, see /etc/sysctl.d/10-ptrace.conf

The etc/sysctl.d/10-ptrace.conf file simply states:

A PTRACE scope of "0" is the more permissive mode.

This is exactly what I have, see above. Is there any reason why this should fail? Or is this a bug?

Answer 1

The kworker "process" that you show is a kernel thread and not a normal process. There is no userspace portion for it and thus no syscalls. Even if it worked it couldn't possibly show anything.

On top of everything else, I guess that tracing kernel threads (under whatever fictional scenario one can imagine) would most probably freeze the system.