we have a doubt on the proper way to terminate a kernel thread that
has been associated to a user process U within a system call with

        kthread_add( .. , .., p, ... )

(p is the struct proc * of the calling process, U)

When U terminates and goes into kern_exit.c :: exit1()
the kernel thread sees the following conditions:

        P_SHOULDSTOP(td->td_proc) is TRUE


We are not sure what is the proper way to terminate
our kernel thread, whose body is the following:

        while (must_run) { // someone will set must_run = 0
                kthread_suspend_check(); // void
                work_or_short_tsleep(); // potentially se

We have seen different ways for the <check_for_forced_termination>

1.      if (P_SHOULDSTOP(td->td_proc)
                break; // kthread_exit() is called outside the loop

2.      if (P_SHOULDSTOP(td->td_proc)
                thread_suspend_check(0); // which then terminates the thread
        // this is done in sys/rpc/svc.c

We are a bit unsure whether calling the thread_*() function in a kthread
is correct -- but there is an example in the kernel.

Variants involve locking td->td_proc (but is it necessary ? The process
won't go away until all child threads die), or checking the td_tdflags
instead of the parent process' flags.

So what is the correct way ?


 Prof. Luigi RIZZO, ri...@iet.unipi.it  . Dip. di Ing. dell'Informazione
 http://www.iet.unipi.it/~luigi/        . Universita` di Pisa
 TEL      +39-050-2217533               . via Diotisalvi 2
 Mobile   +39-338-6809875               . 56122 PISA (Italy)
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