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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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