Re: [fuse-devel] fuse: trying to steal weird page

[Miklos Szeredi <miklos@szeredi.hu>]

On Tue, Feb 26, 2019 at 1:57 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Mon, Feb 25, 2019 at 10:41 PM Nikolaus Rath <Nikolaus@rath.org> wrote:
> >
> > On Feb 12 2019, Nikolaus Rath <Nikolaus@rath.org> wrote:
> > > On Feb 12 2019, Miklos Szeredi <miklos@szeredi.hu> wrote:
> > >> On Sun, Feb 10, 2019 at 11:05 PM Nikolaus Rath <Nikolaus@rath.org> wrote:
> > >>
> > >>> Bad news. I can now reliably reproduce the issue again.
> > >>
> > >> A reliable reproducer is always good news.   Are the messages exactly
> > >> the same as last time (value of flags, etc)?
> > >
> > > The flags, count, mapcount and mapping values are always the same. The
> > > page and index is varying. So the general format is:
> > >
> > > [ 2562.773181] fuse: trying to steal weird page
> > > [ 2562.773187] page=<something> index=<something>
> > > flags=17ffffc00000ad, count=1, mapcount=0, mapping= (null)
> >
> > Is there anything else I can do to help debugging this?
>
> Could you please try the attached patch?

Looking more, it's very unlikely to help.  remove_mapping() should
already ensure that the page count is 1.

I think this bug report needs to be forwarded to the
<linux-mm@kvack.org> mailing list as this appears to be  a race
somewhere in the memory management subsystem and fuse is only making
it visible due to its sanity checking in the page stealing code.

Thanks,
Miklos