linux-kernel - Re: [PATCH 1/10] Add generic helpers for arch IPI function calls

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Date:	Tue, 10 Jun 2008 17:53:08 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, npiggin@...e.de, linux-arch@...r.kernel.org,
	jeremy@...p.org, mingo@...e.hu,
	Russell King <rmk+lkml@....linux.org.uk>
Subject: Re: [PATCH 1/10] Add generic helpers for arch IPI function calls

On Tue, 2008-06-10 at 08:47 -0700, Paul E. McKenney wrote:
> On Tue, Jun 10, 2008 at 03:51:25PM +0100, Catalin Marinas wrote:
> > I was thinking whether this condition can be removed and allow the
> > smp_call_function*() to be called with IRQs disabled. At a quick look,
> > it seems to be possible if the csd_flag_wait() function calls the IPI
> > handlers directly when the IRQs are disabled (see the patch below).
[...]
> There were objections last month:  http://lkml.org/lkml/2008/5/3/167

Thanks, I missed this discussion.

> The issue was that this permits some interrupts to arrive despite
> interrupts being disabled.  There seemed to be less resistance to
> doing this in the wait==1 case, however.

The "(wait == 1) && irqs_disabled()" case is what I would be interested
in. In the patch you proposed, this doesn't seem to be allowed (at least
from the use of WARN_ON). However, from your post in May:

> 5.	If you call smp_call_function() with irqs disabled, then you
> 	are guaranteed that no other CPU's smp_call_function() handler
> 	will be invoked while smp_call_function() is executing.

this would be possible but no one need this functionality yet.

Would one use-case (ARM SMP and DMA cache maintenance) be enough to
implement this or I should add it to the ARM-specific code?

Thanks.

-- 
Catalin

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