On Fri, Apr 15, 2005 at 06:58:20PM +0100, Hugh Dickins wrote:
> > > If there was a fix for the bad pmd problem it might be a candidate
> > > for stable, but so far we dont know what causes it yet.
> > If I figure a way to trigger here, I'll report back.
>
> Dave, earlier on you were quite able to reproduce the problem on 2.6.11,
> finding it happened the first time you ran X. Do you have any time to
> reverify that, then try to reproduce with the load_cr3 in leave_mm patch?
>
> But please don't waste your time on this unless you think it's plausible.
I used to be able to reproduce it 100% by doing this on an vanilla
upstream kernel. Then it changed behaviour so I only saw it happening
on the Fedora kernel. For the latest Fedora update kernel I backported
this change..
- x86_64: Only free PMDs and PUDs after other CPUs have been flushed
as a 'try it and see'. At first I thought it killed the bug, but
a day or so later, it started doing it again.
In the Fedora kernel we have a patch which restricts /dev/mem reading,
so I got suspicious about this interacting with any of the changes
that had happened to drivers/char/mem.c
Out of curiousity, I backported the 3-4 patches from .12rc to
the Fedora .11 kernel, and haven't seen the problem since.
The bizarre thing is I can't explain why any of those patches would
make such a difference. Given the bug seems to be coming and going
for me, its possible its just masked the problem.
Dave
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