mm: Question: pte SMP data race in do_anomyous_page()?

[Karim Manaouil <kmanaouilinux@gmail.com>]

Hi,

In do_anonymous_page(), a new page is allocated and zeroed, and the 
corresponding page struct is initialised (setting flags PageUptodate,
PageSwapBacked, etc. and initialising the various counters).

Then, set_pte_at() is called directly without calling smp_wmb() to make
the updates above visible on other CPUs.

This could race with a page table walker. The walker can read the new pte
and try to access the page struct or the page content before the changes
above were made visible.

The reason I thought about this is because of the comment in
pmd_install(), which describes exactly the same situation, so I
wondered why the same thing is not considered in do_anonymous_page().

I might probably be missing something, but I would love to hear your
comments.

Cheers
Karim