[RFC PATCH RESEND 19/28] mm: disallow do_swap_page to handle page faults under VMA lock

[Suren Baghdasaryan]

On Tue, Sep 6, 2022 at 12:39 PM Peter Xu <peterx at redhat.com> wrote:
>
> On Thu, Sep 01, 2022 at 10:35:07AM -0700, Suren Baghdasaryan wrote:
> > Due to the possibility of do_swap_page dropping mmap_lock, abort fault
> > handling under VMA lock and retry holding mmap_lock. This can be handled
> > more gracefully in the future.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb at google.com>
> > ---
> >  mm/memory.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 9ac9944e8c62..29d2f49f922a 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -3738,6 +3738,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> >       vm_fault_t ret = 0;
> >       void *shadow = NULL;
> >
> > +     if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> > +             ret = VM_FAULT_RETRY;
> > +             goto out;
> > +     }
> > +
>
> May want to fail early similarly for handle_userfault() too for similar
> reason.  Thanks,

I wasn't aware of a similar issue there. Will have a closer look. Thanks!

>
> --
> Peter Xu
>