[linux-audio-dev] ieee1394 deadlock on RT kernels

[Lee Revell]

On Mon, 2006-06-26 at 01:08 +0200, Pieter Palmers wrote:
> Hi,
> 
> We are experiencing 'soft' deadlocks when running our code (Freebob, 
> i.e. userspace lib for firewire audio) on RT kernels. After a few 
> seconds, I get a kernel panic message that signals a soft lockup.
> 

Can we see the kernel panic message? ;-)

Lee

> The problems occur when an ISO stream (receive and/or transmit) is shut 
> down in a SCHED_FIFO thread. More precisely when running the freebob 
> jackd backend in real-time mode. And even more precise: they only seem 
> to occur when jackd is shut down. There are no problems when jackd is 
> run without RT scheduling.
> 
> I havent been able to reproduce this with other test programs that are 
> shutting down streams in a SCHED_FIFO thread.
> 
> printk() debugging point to the tasklet_kill() call in 
> ohci1349_unregister_iso_tasklet (drivers/ieee1394/ohci1394.c), that 
> doesn't seem to return. For experiment, i've put a tasklet_disable 
> before the tasklet_kill, and that causes the soft lockup to be due to 
> the tasklet_disable.
> 
> I would like to ask if anyone has a clue why this is happening. The only 
> thing I can come up with is that jackd is stopped by a CTRL-C, and that 
> the stream shutdown happens in signal handler context, which somehow 
> interacts with the tasklet_kill. But I don't have the time now to dig 
> into this, so for a change I ask for advice early instead of first 
> banging my head against the wall for some days :).
> 
> Thx,
> 
> Pieter Palmers
> 
>