Re: [PATCH] mm/mprotect: fix compilation warning because of unused 'mm' varaible

[Song Liu <liu.song.a23@xxxxxxxxx>]

On Mon, May 13, 2019 at 4:51 PM Song Liu <liu.song.a23@xxxxxxxxx> wrote:
>
> On Wed, May 8, 2019 at 4:50 AM Mike Rapoport <rppt@xxxxxxxxxxxxx> wrote:
> >
> > Since commit 0cbe3e26abe0 ("mm: update ptep_modify_prot_start/commit to
> > take vm_area_struct as arg") the only place that uses the local 'mm'
> > variable in change_pte_range() is the call to set_pte_at().
> >
> > Many architectures define set_pte_at() as macro that does not use the 'mm'
> > parameter, which generates the following compilation warning:
> >
> >  CC      mm/mprotect.o
> > mm/mprotect.c: In function 'change_pte_range':
> > mm/mprotect.c:42:20: warning: unused variable 'mm' [-Wunused-variable]
> >   struct mm_struct *mm = vma->vm_mm;
> >                     ^~
> >
> > Fix it by passing vma->mm to set_pte_at() and dropping the local 'mm'
> > variable in change_pte_range().
> >
> > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > ---
> >  mm/mprotect.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > index 028c724..61bfe24 100644
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -39,7 +39,6 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> >                 unsigned long addr, unsigned long end, pgprot_t newprot,
> >                 int dirty_accountable, int prot_numa)
> >  {
> > -       struct mm_struct *mm = vma->vm_mm;
> >         pte_t *pte, oldpte;
> >         spinlock_t *ptl;
> >         unsigned long pages = 0;
> > @@ -136,7 +135,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> >                                 newpte = swp_entry_to_pte(entry);
> >                                 if (pte_swp_soft_dirty(oldpte))
> >                                         newpte = pte_swp_mksoft_dirty(newpte);
> > -                               set_pte_at(mm, addr, pte, newpte);
> > +                               set_pte_at(vma->mm, addr, pte, newpte);
>
> This should be vma->vm_mm.

And we need to fix another reference to mm:

diff --git i/mm/mprotect.c w/mm/mprotect.c
index 8bdba81685d6..bf38dfbbb4b4 100644
--- i/mm/mprotect.c
+++ w/mm/mprotect.c
@@ -135,7 +135,7 @@ static unsigned long change_pte_range(struct
vm_area_struct *vma, pmd_t *pmd,
                                newpte = swp_entry_to_pte(entry);
                                if (pte_swp_soft_dirty(oldpte))
                                        newpte = pte_swp_mksoft_dirty(newpte);
-                               set_pte_at(vma->mm, addr, pte, newpte);
+                               set_pte_at(vma->vm_mm, addr, pte, newpte);

                                pages++;
                        }
@@ -149,7 +149,7 @@ static unsigned long change_pte_range(struct
vm_area_struct *vma, pmd_t *pmd,
                                 */
                                make_device_private_entry_read(&entry);
                                newpte = swp_entry_to_pte(entry);
-                               set_pte_at(mm, addr, pte, newpte);
+                               set_pte_at(vma->vm_mm, addr, pte, newpte);

                                pages++;
                        }