[PATCH] mm: lock newly mapped VMA with corrected ordering

[Suren Baghdasaryan]

On Sat, Jul 8, 2023 at 4:10 PM Suren Baghdasaryan <surenb at google.com> wrote:
>
> On Sat, Jul 8, 2023 at 4:04 PM Hugh Dickins <hughd at google.com> wrote:
> >
> > Lockdep is certainly right to complain about
> > (&vma->vm_lock->lock){++++}-{3:3}, at: vma_start_write+0x2d/0x3f
> >                but task is already holding lock:
> > (&mapping->i_mmap_rwsem){+.+.}-{3:3}, at: mmap_region+0x4dc/0x6db
> > Invert those to the usual ordering.
>
> Doh! Thanks Hugh!
> I totally forgot to run this with lockdep enabled :(

I verified both the lockdep warning and the fix. Thanks again, Hugh!

Tested-by: Suren Baghdasaryan <surenb at google.com>

>
> >
> > Fixes: 33313a747e81 ("mm: lock newly mapped VMA which can be modified after it becomes visible")
> > Cc: stable at vger.kernel.org
> > Signed-off-by: Hugh Dickins <hughd at google.com>
> > ---
> >  mm/mmap.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 84c71431a527..3eda23c9ebe7 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2809,11 +2809,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >         if (vma_iter_prealloc(&vmi))
> >                 goto close_and_free_vma;
> >
> > +       /* Lock the VMA since it is modified after insertion into VMA tree */
> > +       vma_start_write(vma);
> >         if (vma->vm_file)
> >                 i_mmap_lock_write(vma->vm_file->f_mapping);
> >
> > -       /* Lock the VMA since it is modified after insertion into VMA tree */
> > -       vma_start_write(vma);
> >         vma_iter_store(&vmi, vma);
> >         mm->map_count++;
> >         if (vma->vm_file) {
> > --
> > 2.35.3