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On Sun, 3 Sep 2000, Rik van Riel wrote:

> On Sun, 3 Sep 2000, Linus Torvalds wrote:
> >
> > What you're saying is that you're ignoring the evidence because you don't
> > like it and you don't understand how it happens.
> >
> > The BUG() was "impossible", so you're discounting it?
> >
> > I can tell you several ways it happens in.
> > - modify the page after free_page(). free_page() won't see bad
> > state, but alloc_page() will.
>
> __alloc_pages() didn't see it either, but Christian seems
> to have found a possible cause for the bug (as you got by
> private email).

Well, the bug seems to exactly using the page after a "free_page()". Which
is always a bug, but at least should be easy to fix.

I've considered making "free_page()" a macro something like

__free_pge(x);
x = NULL;

but that works only for lvalues, of course, and not all users are
lvalue-users, so it's hard to do. But that would have caught this.

Linus

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