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Date: Thu, 20 Mar 2003 12:47:01 +0100
From: Maarten Ghijsen <maarten.ghijsen@planet.nl>
Subject: wake_up call from IRQ handler freezes system (no Oops)
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Hello,

I am designing a linux driver for a DVB/ASI PCI card. 

One of the IOCTL commands implemented in my driver allows the user to
transfer a buffer to the PCI card (using DMA). While the DMA is in progress
I want to sleep the user process/thread. For the sleeping I use the
wait_event function, which waits for an event that is 'fired' from the DMA
done interrupt (with wake_up call). As soon as the interrupt handler calls
the wake_up my system freezes completely, without any Oops or other
exception message. 

As far as I can gather from the linux device driver book and other sources
from drivers it is common practice to use a wake_up in the interrupt routine
to awaken any sleeping user threads. I am pretty sure that I have
initialised my wait_queue_head_t correctly with a call to
init_waitqueue_head.

Does anyone have any idea why the system hangs on the wake-up from the
interrupt handler?

Below you will find some pseudo code for with the wait_event and the
wake_up:

// wait from DMA IOCTL handler
void Dta1xxTxIoCtlDma()
{
	startdma();

	wait_event(my_wait_queue, ( 1==dma_done_flag) );

	return;
}

// wake_up from interrupt handler
void Dta1xxIRQ()
{
	if ( IsDmaDoneInterruptSet() ) {
		dma_done_flag = 1;
		wake_up(&my_wait_queue);
	}
}

I am using linux kernel version 2.4.18.

Regards,
 
Maarten