From: Steven Rostedt <rostedt@goodmis.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 2/4] nmi: add generic nmi tracking state
Date: Fri, 6 Feb 2009 12:22:10 -0500 (EST) [thread overview]
Message-ID: <alpine.DEB.1.10.0902061216370.22636@gandalf.stny.rr.com> (raw)
In-Reply-To: <20090206091039.d0acb680.akpm@linux-foundation.org>
On Fri, 6 Feb 2009, Andrew Morton wrote:
> >
> > That would be fun to implement. Not the in_nmi code, but the handling of
> > nested NMIs. How would you be able to save the state when the NMI occurred
> > without being preempted by another NMI?
>
> Like with normal interrupts?
Normal interrupts can enable interrupts again, while in the handler, as
well as disable them.
>
> As long as the number of sources is finite, nested NMIs could work OK.
I guess you would need a mechanism to enable and disable NMIs.
>
> > I think the arch that has nested NMIs will have many more issues to solve
> > in the kernel than this one.
>
> I have a vague memory that x86 can do this.
>
> <googles a bit>
>
> What's all this about?
> https://www.x86-64.org/pipermail/discuss/2005-October/007010.html
Yuck, masking Non Maskable Interrupts?
> http://kerneltrap.org/index.php?q=mailarchive/linux-kernel/2008/2/12/830704/thread
It looks like it calls nmi_exit, so the code would dec it.
>
> I expect that even if it is possible, we can live without it.
>
> And if I'm wrong, it'll be easy to accommodate by adding a new counter
> into the task_struct or thread_struct.
Yeah, the bug on would trigger as soon as we do that, and we could
easily update the code when that time comes.
>
> Does your above implementation make in_interrupt() return true if
> in_nmi()? I think it doesn't, but should?
The "in_nmi()" is set when we do nmi_enter, and nmi_enter also calls
irq_enter which makes in_interrupt() true. I thought adding the in_nmi
condition to in_interrupt would be redundant.
-- Steve
next prev parent reply other threads:[~2009-02-06 17:22 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-06 6:53 [PATCH 0/4] ftrace: updates for tip Steven Rostedt
2009-02-06 6:53 ` [PATCH 1/4] ftrace, x86: rename in_nmi variable Steven Rostedt
2009-02-06 6:53 ` [PATCH 2/4] nmi: add generic nmi tracking state Steven Rostedt
2009-02-06 7:12 ` Andrew Morton
2009-02-06 13:25 ` Steven Rostedt
2009-02-06 17:10 ` Andrew Morton
2009-02-06 17:22 ` Steven Rostedt [this message]
2009-02-06 9:34 ` Peter Zijlstra
2009-02-06 14:46 ` Ingo Molnar
2009-02-06 14:50 ` Steven Rostedt
2009-02-06 14:54 ` Ingo Molnar
2009-02-06 14:59 ` Steven Rostedt
2009-02-06 15:16 ` Ingo Molnar
2009-02-06 15:33 ` Frederic Weisbecker
2009-02-06 15:43 ` Ingo Molnar
2009-02-06 6:53 ` [PATCH 3/4] ftrace: change function graph tracer to use new in_nmi Steven Rostedt
2009-02-06 6:53 ` [PATCH 4/4] ring-buffer: use generic version of in_nmi Steven Rostedt
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