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SubjectRe: [BUG] kernel BUG at arch/i386/mm/highmem.c:15! on 2.6.23-rc8/rc9


On Thu, 4 Oct 2007, Hugh Dickins wrote:
>
> Very helpful, thanks. Guru, please try the appended patch, I think
> you'll find it fixes it for you (it did for me, once I'd puzzled out
> why I was failing to reproduce the problem - tests on ext3 don't work).
> Thank you so much for reporting this just in time!

Ouch.

The patch looks obviously correct, to the point that I don't understand
how this bug happened in the first place. It seems to have been
introduced by Nick in d0217ac04ca6591841e5665f518e38064f4e65bd ("mm: fault
feedback #1") if I read it right.

So "do_nonlinear_fault()" would effectively end up unmapping the PTE
twice, right? And if I understand the problem right, this wasn't noticed
immediately, because it probably only matters on:

- CONFIG_HIGHPTE
*and*
- a filesystem that allows VM_NONLINEAR, which became very rare with
dirty accounting.

Correct?

Linus
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