On Mon, Dec 10, 2018 at 03:09:25PM -0500, Andrea Arcangeli wrote:
> Hello,
>
> On Mon, Dec 10, 2018 at 07:51:16PM +0200, Mike Rapoport wrote:
> > On Mon, Dec 10, 2018 at 02:51:21PM +0800, Peter Xu wrote:
> > > When the process being tracked do mremap() without
> > > UFFD_FEATURE_EVENT_REMAP on the corresponding tracking uffd file
> > > handle, we should not generate the remap event, and at the same
> > > time we should clear all the uffd flags on the new VMA. Without
> > > this patch, we can still have the VM_UFFD_MISSING|VM_UFFD_WP
> > > flags on the new VMA even the fault handling process does not
> > > even know the existance of the VMA.
> > >
> > > CC: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > > CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > CC: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> > > CC: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
> > > CC: Hugh Dickins <hughd@xxxxxxxxxx>
> > > CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> > > CC: Pravin Shedge <pravin.shedge4linux@xxxxxxxxx>
> > > CC: linux-mm@xxxxxxxxx
> > > CC: linux-kernel@xxxxxxxxxxxxxxx
> > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> > > ---
> > > fs/userfaultfd.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > > index cd58939dc977..798ae8a438ff 100644
> > > --- a/fs/userfaultfd.c
> > > +++ b/fs/userfaultfd.c
> > > @@ -740,6 +740,9 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
> > > vm_ctx->ctx = ctx;
> > > userfaultfd_ctx_get(ctx);
> > > WRITE_ONCE(ctx->mmap_changing, true);
> > > + } else if (ctx) {
> > > + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > > + vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
>
> Great catch Peter!
>
> >
> > My preference would be
> >
> > if (!ctx)
> > return;
> >
> > if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
> > ...
> > } else {
> > ...
> > }
> >
> > but I don't feel strongly about it.
>
> Yes, it'd look nicer to run a single "ctx not null" check.
I agree.
>
> >
> > I'd appreciate a comment in the code and with it
> >
> > Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> >
>
> Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Thanks to both! I'll repost soon.
Regards,
--
Peter Xu
