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From: Keith Owens <kaos@ocs.com.au>
To: Andrew Morton <akpm@osdl.org>
cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>
Subject: Re: i386 IPI handlers running with hardirq_count == 0 
In-reply-to: Your message of "Thu, 29 Jun 2006 02:18:00 MST."
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Date: Fri, 30 Jun 2006 02:40:38 +1000
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Andrew Morton (on Thu, 29 Jun 2006 02:18:00 -0700) wrote:
>On Thu, 29 Jun 2006 19:01:17 +1000
>Keith Owens <kaos@ocs.com.au> wrote:
>
>> Macro arch/i386/kernel/entry.S::BUILD_INTERRUPT generates the code to
>> handle an IPI and call the corresponding smp_<name> C code.
>> BUILD_INTERRUPT does not update the hardirq_count for the interrupted
>> task, that is left to the C code.  Some of the C IPI handlers do not
>> call irq_enter(), so they are running in IRQ context but the
>> hardirq_count field does not reflect this.  For example,
>> smp_invalidate_interrupt does not set the hardirq count.
>> 
>> What is the best fix, change BUILD_INTERRUPT to adjust the hardirq
>> count or audit all the C handlers to ensure that they call irq_enter()?
>> 
>
>The IPI handlers run with IRQs disabled.  Do we need a fix?

Some IPI handlers issue irq_enter() to bump hard_irq_count, some IPI
handlers do not.  It is inconsistent, with no obvious reason for doing
it either way.  All the external irqs go via do_IRQ which does issue
irq_enter().  I guess that my real question is why are some IPIs not
using irq_enter()?  The lack of consistency concerns me.