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SubjectRe: One more boobytrap needed for 2.2.15pre ?
[cc'ed back to lk]
I have one _idea_ what could have happened:

1) thread is running with TASK_INTERRUPTIBLE
2) calls schedule()
3) schedule calls del_from_runqueue()
4) ...
5) can't find a new task, jumps to recalculate
6) enables interrupts
7) interrupt
8) XXXXXXXXXXXXXX: someone changes current->state from within the interrupt.
current->state now TASK_RUNNING
9) interrupt returns
10) recalculate finishes, jumps to repeat_schedule().
11) prev->state == TASK_RUNNING, so current is selected
12) a task that's not on the runqueue is selected!!!!!!!!!

Ok, but now the question is: which interrupt changes current->state? Perhaps
a special boobytrap in the interrupt handlers could detect that?

in arch/i386/kernel/irq.c:
* store "current->state" in a special local variable.
* always change it to TASK_INTERRUPTIBLE.
* before returning: check if someone changed current->state
* restore the old value.


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