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Date: Fri, 12 May 2006 07:49:29 -0700
From: Andrew Morton <akpm@osdl.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: mingo@elte.hu, markh@compro.net, linux-kernel@vger.kernel.org,
       dwalker@mvista.com, tglx@linutronix.de
Subject: Re: 3c59x vortex_timer rt hack (was: rt20 patch question)
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Steven Rostedt <rostedt@goodmis.org> wrote:
>
>  Use this patch instead.  It needs an irq disable.  But, believe it or not,
>  on SMP this is actually better.  If the irq is shared (as it is in Mark's
>  case), we don't stop the irq of other devices from being handled on
>  another CPU (unfortunately for Mark, he pinned all interrupts to one CPU).
> 
>  Andrew,
> 
>  should this be changed in mainline too?

I suppose so - we're taking the lock with spin_lock_bh(), but it can also
be taken by this CPU from the interrupt, so it'll deadlock.  But lo!  We've
done disable_irq(), so the interrupt won't be happening.

So yes, doing spin_lock_irq() (irqrestore isn't needed in a timer handler)
instead of disable_irq() in vortex_timer() looks OK.

One does wonder how long we'll hold off interrupts though.