On Thu, 26 Jul 2007 16:52:44 -0700 Suleiman Souhlal <[email protected]> wrote:
> make_pages_present() is dirtying mlocked pages if the VMA is writable, even
> though it shouldn't, by telling get_user_pages() to simulate a write fault.
>
> A simple way to test this is to mlock a multi-GB file, and then sync.
> The sync will take a long time.
ugh, how bad of us.
> As far as I can see, it should be safe to just not simulate a write fault.
We pass in "write=1" to force a COW. This is because we want to do all
that memory allocation at mlock()-time, not later on, when the app writes
to the page.
> Signed-off-by: Suleiman Souhlal <[email protected]>
> ---
> mm/memory.c | 5 ++---
> 1 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index f64cbf9..f43c9e8 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2664,18 +2664,17 @@ #endif /* __PAGETABLE_PMD_FOLDED */
>
> int make_pages_present(unsigned long addr, unsigned long end)
> {
> - int ret, len, write;
> + int ret, len;
> struct vm_area_struct * vma;
>
> vma = find_vma(current->mm, addr);
> if (!vma)
> return -1;
> - write = (vma->vm_flags & VM_WRITE) != 0;
> BUG_ON(addr >= end);
> BUG_ON(end > vma->vm_end);
> len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
> ret = get_user_pages(current, current->mm, addr,
> - len, write, 0, NULL, NULL);
> + len, 0, 0, NULL, NULL);
> if (ret < 0)
> return ret;
> return ret == len ? 0 : -1;
So something sterner will need to be done. I guess the write_access arg to
handle_mm_fault() would need to become a three-value thing.
-
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