Arthur Naseef wrote:
>
> All:
>
> I have been diagnosing kernel panics for over a week and I have
> concerns with the use of tq_scheduler for which I was hoping I
> could get some assistance.
>
> Is it considered acceptable for functions in the tq_scheduler
> task list to call schedule? Is it acceptable for such functions
> to wait on wait queues? What limitations exist?
When a task wants to exit, it cleans up all its stuff,
sets its state to TASK_ZOMBIE and then calls schedule().
The scheduler takes it off the runqueue and the task
is never again executed. It's just a couple of stack
pages which are waiting for someone in wait4() to release.
But imagine what happens if the TASK_ZOMBIE task hits
schedule() and finds a tq_scheduler task to run. And that
task calls schedule(). In state TASK_ZOMBIE. Messy.
At the very least, the schedule() call will never return.
If the tq_scheduler task sets current->state to
TASK_[UN]INTERRUPTIBLE (as it should) before calling
schedule() then it has overwritten TASK_ZOMBIE and the
task which is trying to exit has become magically
resurrected. As far as I can tell, the "dead" task
will run again, do the `fake_volatile' thing in do_exit()
and try to go zombie again.
It would be very interesting to change the test in
schedule():
sti();
- if (tq_scheduler)
+ if (tq_scheduler && current->state != TASK_ZOMBIE)
goto handle_tq_scheduler;
It's all rather unpleasant, and tq_scheduler was killed
in 2.4. I suggest you take a look at all the serial
drivers in 2.4, see how I converted them to use schedule_task().
Someone kindly ported schedule_task() to 2.2.recent, so you
should be able to use that in the same way.
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This archive was generated by hypermail 2b29 : Thu May 31 2001 - 21:00:38 EST