RE: O(1) scheduler seems to lock up on sched_FIFO and sched_RR ta

[Perez-Gonzalez, Inaky]

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Hi All

I have another test case that is showing this behavior.
It is very similar to George's, however, it is a simplification
of another one using threads that a co-worker, Adam Li found
a few days ago.

Parent (FIFO 5) forks child that sets itself to FIFO 4 and=20
busy loops, then it sleeps five seconds and kills the child.=20

Doing SysRq + T after a while shows the parent'd call trace=20
to be at sys_rt_sigaction+0xd1, that is just inside the final=20
copy_to_user() in signal.c:sys_rt_sigaction().

Reprioritizing events/0 to FIFO 5+ fixes the inversion.=20

If I call nanosleep directly (with system() instead of
glibc's sleep(), so I avoid all the rt_sig calls),
I get the parent process always stuck in work_resched+0x5,
in entry.S:work_resched, just after the call to the
scheduler - however, I cannot trace what is happening
inside the scheduler.

My point here is: I am trying to trace where this program
is making use of workqueues inside of the kernel, and I
can find none. The only place where I need to look some
more is inside the timer code, but in a quick glance,
it seems it is not being used, so why is it affected by
the reprioritization of the events/0 thread? George, can
you help me here?

kernel is 2.5.67, SMP and PREEMPT with maxcpus=3D1; tomorrow
I will try .72 ...=20

I=F1aky P=E9rez-Gonz=E1lez -- Not speaking for Intel -- all opinions =
are my own
(and my fault)

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#include <signal.h>=0A=
#include <unistd.h>=0A=
#include <linux/unistd.h>=0A=
#include <stdlib.h>=0A=
#include <sched.h>=0A=
#include <stdio.h>=0A=
#include <time.h>=0A=
=0A=
volatile int dummy;=0A=
volatile int child_run =3D 1;=0A=
=0A=
/* #define DPRINTF(a...) fprintf(stderr, a) */=0A=
#define DPRINTF(a...) do { } while (0)=0A=
=0A=
void child_signal_handler (int signum)=0A=
{=0A=
  child_run =3D 0;=0A=
}=0A=
=0A=
int main (void)=0A=
{=0A=
  int child;=0A=
  struct timespec tp =3D { 5, 0 };=0A=
  struct sched_param param;=0A=
  param.sched_priority =3D 5;=0A=
  sched_setscheduler (0, SCHED_FIFO, &param);=0A=
  child =3D fork();=0A=
  switch (child)=0A=
  {=0A=
   case 0:=0A=
    DPRINTF("Child starts\n");=0A=
    signal (SIGTERM, child_signal_handler);=0A=
    param.sched_priority =3D 4;=0A=
    sched_setscheduler (0, SCHED_FIFO, &param);=0A=
    for (; child_run;)=0A=
      dummy =3D dummy + 1;=0A=
    DPRINTF("Child dies\n");=0A=
    break;=0A=
   case -1:=0A=
    perror ("fork failed");=0A=
    abort();=0A=
    break;    =0A=
   default:=0A=
/*     sleep (5); */=0A=
    syscall (__NR_nanosleep, &tp, NULL);=0A=
    kill (child, SIGTERM);=0A=
   break;=0A=
  }=0A=
  return 0;=0A=
}=0A=
=0A=
    =0A=
  =0A=

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