Re: [PATCH] SCSI: Replace semaphores with wait_even

[Ingo Molnar <mingo@elte.hu>]

* James Bottomley <James.Bottomley@SteelEye.com> wrote:

> On Sun, 2004-10-24 at 16:06, Thomas Gleixner wrote:
> > Hmm, strange. It works on two systems here and others using this
> > modification had no problem either. 
> > I will check again.
> 
> Yes, very strange given what the mistake is:
> 
> -               down_interruptible(&sem);
> +               wait_event_interruptible(eh_wait, shost->eh_kill ||
> +                               (shost->host_busy ==
> shost->host_failed));
> 
> This condition is always true when the eh thread first starts because
> the default quiescent state of a scsi host is
> 
> shost->host_busy = shost->host_failed = 0
> 
> so your change makes the eh_thread spin forever locking everything
> else off the CPU.  On a UP system, this is a complete hang.

i think i fixed this in my PREEMPT_REALTIME tree (having seen spinning
eh_threads) - maybe Thomas forgot to merge those fixes back?

(in a PREEMPT_REALTIME kernel a spinning thread is just a thread eating
up CPU power, it doesnt cause a hang.)

	Ingo