Re: Buggy IPI and MTRR code on low memory

From: Steven Rostedt
Date: Wed Jan 28 2009 - 13:34:25 EST

On Wed, 28 Jan 2009, Arjan van de Ven wrote:

> On Wed, 28 Jan 2009 12:24:48 -0500 (EST)
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > > ---
> > I'll have skip the NMI test and see if it locks up any place else.
> if you get an NMI during MTRR changing you are more or less screwed.
> Really. (the cpu is uncachable etc)

Heh, the NMI is just another place that has the IPI problem. A different
issue to the MTRR. Well, same bug, different place.

> the MTRR code should disable NMIs as much as possible.
> and for sure in -RT, the MTRR change section should not be preemptable
> at all.

Yeah, that is why I found this. The current code calls kfree and such from
the IPI if it is allocated (not to mention the kmalloc in
smp_call_function. Both of which can sleep in RT. I was forcing the
data=NULL case in RT to keep it from entering the allocation code paths.
But this is where I found the deadlock with MTRR (and NMI).

-- Steve

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