Re: [rtl] OS questions

[Sven Heursch <Sven.Heursch@unibw-muenchen.de>]

David Olofson wrote:

>
>
> > I am using a kill_proc() to send a signal to a standard linux user process.
> > It seems to me to work fine.
>
> From include/linux/sched.h:
>
> #define for_each_task(p) \
>         for (p = &init_task ; (p = p->next_task) != &init_task ; )
>
> What happens if Linux is in the middle of removing or inserting a task
> just before of after the task you're sending the signal to when you come
> in preemting it?
>
> Also, from /kernel/exit.c, in function send_sig():
>
>         save_flags(flags); cli();
>         if ((sig == SIGKILL) || (sig == SIGCONT)) {
>                 if (p->state == TASK_STOPPED)
>                         wake_up_process(p);
>                 p->exit_code = 0;
>                 p->signal &= ~( (1<<(SIGSTOP-1)) | (1<<(SIGTSTP-1)) |
>                                 (1<<(SIGTTIN-1)) | (1<<(SIGTTOU-1)) );
>         }
>         if (sig == SIGSTOP || sig == SIGTSTP || sig == SIGTTIN || sig ==
> SIGTTOU)
>                 p->signal &= ~(1<<(SIGCONT-1));
>         restore_flags(flags);
>
> The cli() has no effect on RTL tasks/ISRs... You'll get away with it
> most of the time, but it's not safe.

Yes thx, I understand this, but it works fine with the kill_proc() call within
the RT-ISR. Or do you have a better idea, how to send a signal to a linux process
from within a RT-ISR?

A last question:

When an interrupt occurs and the ISR starts and ends after a while, is there a
schedule() call or is only the variable resched set ?
If not, how does the timerinterrupt motivate the scheduler to schedule an event
NOW?

TIA
S. Heursch


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