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SubjectIs a process with a priority of 0 legal ?


If it is the 2.2.16 scheduler & other linux'es have a bug.

The following code snippets can go into a tight loop.
while (p != &init_task)
{
if (can_schedule(p))
{
int weight = goodness(prev, p, this_cpu);
if (weight > c)
c = weight, next = p;
}
p = p->next_run;
}

/* Do we need to re-calculate counters? */
if (!c)
goto recalculate;



recalculate:
{
struct task_struct *p;
spin_unlock_irq(&runqueue_lock);
read_lock(&tasklist_lock);
for_each_task(p)
p->counter = (p->counter >> 1) + p->priority;
read_unlock(&tasklist_lock);
spin_lock_irq(&runqueue_lock);
goto repeat_schedule;
}

If the weight & priority of all runnable processes is 0 then the
recalculate with recalculate p->counter=0 for all runnable processes,
& the code will go into a tight loop between the goodness calculation &
recalculate.

Not very robust in my opinion.


D.J. Barrow Linux for S/390 kernel developer
eMail: djbarrow@de.ibm.com,barrow_dj@yahoo.com
Phone: +49-(0)7031-16-2583
IBM Germany Lab, Schönaicherstr. 220, 71032 Böblingen


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