You have a race condition.
> int flagvar = 0;
> struct semaphore blocking_sem;
>
> void function_called_from_kernel_thread(void)
> {
> chew_on_hardware();
^^^^^^^^^^^^^^^^^^^^^^^
As soon as you do/did this, the IRQ must've happened. So, before the next
statement is executed, the IRQ handler is called which clears flagvar.
> flagvar = 1;
This is executed _after_ the IRQ handler completes. So, you stomp over
whatever
the IRQ handler did.
> down(blocking_sem);
Since the IRQ handler did up(), this down() won't sleep.
Try setting flagvar = 1 _before_ you chew_on_hardware().
Make sure that what ever you do is SMP safe.
Store the tick count of when you do the IRQ handler and when you do
chew_on_hardware(). You'll see if I am right.
i.e., try:
before = system_ticks_NOW
flagvar = 1;
chew_on_hardware ();
after = system_ticks_NOW
printk (..., before, after, irq)
....
interrupt_handler ( ..)
{
irq = system_ticks_NOW
...
}
Cheers,
-Sudhi.
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