Re: [Xen-devel] vmalloc_sync_all crash still happening on some machines

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.12.11 at 18:15, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> The actual bug you are seeing is hitting the                 
>       BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k))
> towards the end of vmalloc_sync_one(). David, do you remember from when
> you were digging into this stuff what it actually means?

This means that the pmd entry in the reference page tables (init_mm's)
is referencing a different page than the (non-blank) one in the page
table being updated, i.e. some race occurred that allowed two distinct
page tables to be allocated for the same kernel address (range).

If this is reproducible in some way, printing the entries (or really just
their PFNs/MFNs) might help understand what is going on here
(assuming that such a race can be expected to not really exist in
this old and mature a kernel).

Jan


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