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    SubjectRe: Race between vmtruncate and mapped areas?
    On Tuesday, May 13, 2003 16:11:39 -0700 William Lee Irwin III <wli@holomorphy.com> wrote:
    >> Okay, what's stopping filemap_nopage() from fetching the page from
    >> pagecache after one of the mm->mmap_sem's is dropped but before
    >> truncate_inode_pages() removes the page? The fault path is only locked
    >> out for one mm during one part of the operation. I can see taking
    >> ->i_sem in do_no_page() fixing it, but not ->mmap_sem in vmtruncate()
    >> (but of course that's _far_ too heavy-handed to merge at all).

    On Tue, May 13, 2003 at 06:16:16PM -0500, Dave McCracken wrote:
    > mmap_sem is held for read across the entire fault, so by the time
    > vmtruncate_list() can call zap_page_range() the page has been instantiated
    > in the page table and will get removed.

    That's not quite the answer, inode->i_size is.

    The mmap_sem works because then ->i_size can't be sampled by
    filemap_nopage() before the pagetable wiping operation starts.


    -- wli
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