Hello,

I'm trying to create a kernel level mechanism that freezes processes.
So far I've been successful in doing so in some cases but whenever I have
a process running in kernel mode, this mechanism fails.

More precisely I have an Android app that launches two java.lang.Process
instances where each of which issue a shell ping command.
At this point I can see that the app and both processes are in the
sleeping state (S), meaning that their processes are in kernel mode, and
waiting for some syscall to terminate (possibly recvmsg or sendmsg).
In the kernel, I send a signal (SIGSTOP) to one of the ping processes to
freeze it.
I then check the state of the process and I can see that it actually
transitioned from the sleeping to the stopped state (T).
However, when I use strace on that ping process, it shows continuous
socket activity, which means that despite the state of the process, the
signal had no effect on the ping process's kernel level execution.

I would like to know if anyone can help me answer two questions:
Is this behavior normal?
Is there a way to freeze kernel level execution such as a system call?

Linux kernel: goldfish 3.4
Android: KitKat 4.4 r1.2

Thank you very much in advance
Best Regards
pfreezer