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    SubjectRe: invalidate_inode_pages2
    On Tue, May 18, 2004 at 05:27:18PM -0700, Andrew Morton wrote:
    > Andrea Arcangeli <andrea@suse.de> wrote:
    > >
    > > Something broke in invalidate_inode_pages2 between 2.4 and 2.6, this
    > > causes malfunctions with mapped pages in 2.6.
    >
    > What is the malfunction?

    From Olaf Kirch

    - single application on NFS client opens file and maps it.
    No-one else has this file open. File contains "zappa\n",
    and the test app stats it once a second and reports size and
    contents.
    len=6, data=7a 61 70 70 61 0a
    - on the NFS server, I do "echo frobnorz > file"
    - after a while, the test app on the client reports
    len=10, data=7a 61 70 70 61 0a
    - I ctrl-C the app and restart it. We agree that this amounts to
    a munmap+mmap of the file, right?
    The test app now reports
    len=10, data=7a 61 70 70 61 0a 00 00 00 00

    my fix is untested at this time (but I expect it to fix the above
    problem).

    > > I guess the below untested one liner should be enough to fix it. The
    > > only single point of invalidate_inode_pages2, is to invalidate _mapped_
    > > pages too. Otherwise we could as well use invalidate_inode_pages.
    > > Clearly the dirty bit doesn't mean invalidate, invalidate primarly means
    > > clearing the uptodate bitflag.
    > >
    > > --- sles/mm/truncate.c.~1~ 2004-05-18 19:24:40.000000000 +0200
    > > +++ sles/mm/truncate.c 2004-05-19 02:09:28.311781864 +0200
    > > @@ -260,9 +260,10 @@ void invalidate_inode_pages2(struct addr
    > > if (page->mapping == mapping) { /* truncate race? */
    > > wait_on_page_writeback(page);
    > > next = page->index + 1;
    > > - if (page_mapped(page))
    > > + if (page_mapped(page)) {
    > > + ClearPageUptodate(page);
    > > clear_page_dirty(page);
    > > - else
    > > + } else
    > > invalidate_complete_page(mapping, page);
    > > }
    > > unlock_page(page);
    >
    > It's currently the case that pages which are mapped into process pagetables
    > are always up to date, which sounds like a good invariant to have. This

    I already intentionally broke that invariant in 2.4 just to make exactly
    this thing work safely, this is needed for correct O_DIRECT semantics
    too.

    All it matters is that the pages are re-read after munmap+mmap.

    > changes that rule. I dunno if it'll break anything though.

    It didn't break anything in 2.4 AFIK.
    -
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