Messages in this thread |  | | | Date | Tue, 29 May 2001 12:27:59 +1000 | | From | Andrew Morton <> | | Subject | Re: Kernel 2.2: tq_scheduler functions scheduling and waiting |
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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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