Re: oops in copy_page_rep()

[Linus Torvalds <torvalds@linux-foundation.org>]

On Tue, Jan 8, 2013 at 9:30 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> Check difference between patch above and merged one -- a1dd450.
> Merged patch is obviously broken: huge_pmd_set_accessed() can be called
> only if the pmd is under splitting.

Ok, that's a totally different issue, and seems to be due to different
versions (Andrew - any idea why

  http://lkml.org/lkml/2012/10/25/402

and commit a1dd450bcb1a ("mm: thp: set the accessed flag for old pages
on access fault") are different?

That said, I actually think that commit a1dd450bcb1a is correct:
huge_pmd_set_accessed() can not *possibly* need to check the splitting
issue, since it takes the page table lock and re-verifies that the pmd
entry is identical, before just setting the access flags.

So that whole thing is irrelevant. huge_pmd_set_accessed() almost
certainly simply doesn't care about splitting.

But look at commit d10e63f29488. That's the one that removes
pmd_trans_splitting() entirely, and does it for the case that *does*
seem to care, namely do_huge_pmd_wp_page().

                 Linus

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