Re: invalidate_inode_pages2

From: Andrew Morton
Date: Tue May 18 2004 - 20:02:09 EST


Andrea Arcangeli <andrea@xxxxxxx> wrote:
>
> On Tue, May 18, 2004 at 05:27:18PM -0700, Andrew Morton wrote:
> > Andrea Arcangeli <andrea@xxxxxxx> 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

OK. Can we do a full pte invalidation and force a major fault?

> > 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.

It might have caused some of the debug checks in fs/buffer.c to get angry
when it's used by direct-IO. But they're gone now anyway...


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