Re: [PATCH] mm: get_user_pages(write,force) refuse to COW in shared areas

From: Hugh Dickins
Date: Fri Apr 04 2014 - 10:54:11 EST

On Fri, 4 Apr 2014, Kirill A. Shutemov wrote:
> There's comment in do_wp_page() which is not true anymore with patch
> applied. It should be fixed.

The * Only catch write-faults on shared writable pages,
* read-only shared pages can get COWed by
* get_user_pages(.write=1, .force=1).

Yes, I went back and forth on that: I found it difficult to remove that
comment without also simplifying the VM_WRITE|VM_SHARED test immediately
above it, possibly even looking again at the ordering of those tests.

In the end I decided to leave changing it to when we do the other
little cleanups outside get_user_pages(), after it's become clear
whether the new EFAULT is troublesome or not. Most of my testing
had been without any change in do_wp_page(), so I left that out.

> Otherwise, looks good to me:
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

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