From: Mark Gross <mgross@linux.intel.com>
Organization: Intel
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: queue_work from interrupt Real time preemption2.6.11-rc2-RT-V0.7.37-03
Date: Tue, 15 Feb 2005 10:06:44 -0800
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Cc: Steven Rostedt <rostedt@goodmis.org>, LKML <linux-kernel@vger.kernel.org>
References: <200502141240.14355.mgross@linux.intel.com> <200502141429.11587.mgross@linux.intel.com> <20050215104153.GB19866@elte.hu>
In-Reply-To: <20050215104153.GB19866@elte.hu>
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On Tuesday 15 February 2005 02:41, Ingo Molnar wrote:
> * Mark Gross <mgross@linux.intel.com> wrote:
> > On Monday 14 February 2005 13:24, Steven Rostedt wrote:
> > > On Mon, 2005-02-14 at 12:40 -0800, Mark Gross wrote:
> > > > I'm working on a tweak to the preepmtive soft IRQ implementation
> > > > using work queues and I'm having problems with a BUG assert when
> > > > trying to queue_work.
> > > >
> > > > Souldn't I be able to call queue_work form ISR context?
> > >
> > > Yes, but not with interrupts disabled.
> >
> > Hmm.  It seems to me that one should be able to call queue_work from
> > wherever you can call raise_softirq.  This constraint adds a bit of
> > asymetry in the deffered processing API's
>
> one solution is to use the local_irq_*_nort() API variants - but it all
> depends on why you had to disable interrupts.

I'm attempting to change the softIRQ preemption implementation to use work 
queues (one per softIRQ), that allow for runtime priority changes on a 
per-soft IRQ bases.  To do this I was trying to have raise_softirq call 
queu_work directly.  queue_work, doesn't use the *_nort() api's.

My alternitive is to put the call to queue_work into do_softIRQ.  Which seems 
to  work, but feels like a bit too much indirection to queue up the soft IRQ 
bottom half processing.


>
> Almost always irq-disabling done in conjunction with spinlocks, and the
> spin_lock_irq*() variants do not disable interrupts on PREEMPT_RT. I
> kept the assymetry of the local_irq*() APIs because in most cases they
> are used directly interrupts need to be disabled.
>
> it is also the more conservative approach, since we'll get messages like
> the ones you got when it's unsafe to do it - while if local_irq_*() APIs
> didnt disable interrupts we'd never know about the cases when they
> _must_ be disabled.)
>
> but yes, there's some API assymetry - which mostly comes from the fact
> alone that 99.999% of the kernel is now preemptible. There's just so
> much we can do to pretend that this is good'old Linux kernel semantics
>
> :-)
>
> 	Ingo

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