Re: [PATCH v7 06/17] mm/nommu: fix the last places where vma is not locked before being attached

Suren Baghdasaryan
2025-01-07T18:05:37Z

On Tue, Jan 7, 2025 at 9:51 AM Liam R. Howlett <Liam.Howlett@oracle.com> wrote:
>
> * Suren Baghdasaryan <surenb@google.com> [241226 12:07]:
> > nommu configuration has two places where vma gets attached to the vma tree
> > without write-locking it. Add the missing locks to ensure vma is always
> > locked before it's attached.
>
> Does the delete side need to write lock as well?

Ugh. I just realized that CONFIG_PER_VMA_LOCK depends on CONFIG_MMU,
so this patch is not needed because all these per-vma functions are
NoOps when CONFIG_PER_VMA_LOCK=n. I'll drop it in the next version.

>
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> > mm/nommu.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/mm/nommu.c b/mm/nommu.c
> > index 72c8c505836c..1754e84e5758 100644
> > --- a/mm/nommu.c
> > +++ b/mm/nommu.c
> > @@ -1189,6 +1189,7 @@ unsigned long do_mmap(struct file *file,
> > goto error_just_free;
> >
> > setup_vma_to_mm(vma, current->mm);
> > + vma_start_write(vma);
> > current->mm->map_count++;
> > /* add the VMA to the tree */
> > vma_iter_store(&vmi, vma, true);
> > @@ -1356,6 +1357,7 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >
> > setup_vma_to_mm(vma, mm);
> > setup_vma_to_mm(new, mm);
> > + vma_start_write(new);
> > vma_iter_store(vmi, new, true);
> > mm->map_count++;
> > return 0;
> > --
> > 2.47.1.613.gc27f4b7a9f-goog
> >