On Fri, 2017-08-11 at 09:36 -0700, Mike Kravetz wrote:
> On 08/11/2017 08:23 AM, Rik van Riel wrote:
> > On Thu, 2017-08-10 at 17:23 +0200, Michal Hocko wrote:
> > > On Sun 06-08-17 10:04:25, Rik van Riel wrote:
> > > [...]
> > > > diff --git a/kernel/fork.c b/kernel/fork.c
> > > > index 17921b0390b4..db1fb2802ecc 100644
> > > > --- a/kernel/fork.c
> > > > +++ b/kernel/fork.c
> > > > @@ -659,6 +659,13 @@ static __latent_entropy int
> > > > dup_mmap(struct
> > > > mm_struct *mm,
> > > > tmp->vm_flags &= ~(VM_LOCKED |
> > > > VM_LOCKONFAULT);
> > > > tmp->vm_next = tmp->vm_prev = NULL;
> > > > file = tmp->vm_file;
> > > > +
> > > > + /* With VM_WIPEONFORK, the child gets an empty
> > > > VMA. */
> > > > + if (tmp->vm_flags & VM_WIPEONFORK) {
> > > > + tmp->vm_file = file = NULL;
> > > > + tmp->vm_ops = NULL;
> > > > + }
> > >
> > > What about VM_SHARED/|VM)MAYSHARE flags. Is it OK to keep the
> > > around?
> > > At
> > > least do_anonymous_page SIGBUS on !vm_ops && VM_SHARED. Or do I
> > > miss
> > > where those flags are cleared?
> >
> > Huh, good spotting. That makes me wonder why the test case that
> > Mike and I ran worked just fine on a MAP_SHARED|MAP_ANONYMOUS VMA,
> > and returned zero-filled memory when read by the child process.
>
> Well, I think I still got a BUG with a MAP_SHARED|MAP_ANONYMOUS vma
> on
> your v2 patch. Did not really want to start a discussion on the
> implementation until the issue of exactly what VM_WIPEONFORK was
> supposed
> to do was settled.
It worked here, but now I don't understand why :)
> >
> > OK, I'll do a minimal implementation for now, which will return
> > -EINVAL if MADV_WIPEONFORK is called on a VMA with MAP_SHARED
> > and/or an mmapped file.
> >
> > It will work the way it is supposed to with anonymous MAP_PRIVATE
> > memory, which is likely the only memory it will be used on, anyway.
> >
>
> Seems reasonable.
>
> You should also add VM_HUGETLB to those returning -EINVAL. IIRC, a
> VM_HUGETLB vma even without VM_SHARED expects vm_file != NULL.
In other words (flags & MAP_SHARED || vma->vm_file) would catch
hugetlbfs, too?
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
