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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Fri, 9 Sep 2022 09:28:13 -0700
Message-ID: <CAJuCfpH-YQYCQtzWdR9rGfXBD53ZSawXnj-FbuEGqTSd4Y1zmg@mail.gmail.com>
Subject: Re: [RFC PATCH RESEND 14/28] mm: mark VMAs as locked before isolating them
To:     Laurent Dufour <ldufour@linux.ibm.com>
Cc:     akpm@linux-foundation.org, michel@lespinasse.org,
        jglisse@google.com, mhocko@suse.com, vbabka@suse.cz,
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        willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org,
        laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org,
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On Fri, Sep 9, 2022 at 6:35 AM Laurent Dufour <ldufour@linux.ibm.com> wrote=
:
>
> Le 01/09/2022 =C3=A0 19:35, Suren Baghdasaryan a =C3=A9crit :
> > Mark VMAs as locked before isolating them and clear their tree node so
> > that isolated VMAs are easily identifiable. In the later patches page
> > fault handlers will try locking the found VMA and will check whether
> > the VMA was isolated. Locking VMAs before isolating them ensures that
> > page fault handlers don't operate on isolated VMAs.
>
> Found another place where the VMA should probably mark locked:
> *** drivers/gpu/drm/drm_vma_manager.c:
> drm_vma_node_revoke[338]       rb_erase(&entry->vm_rb, &node->vm_files);

Thanks! I'll add the necessary locking.

>
> There are 2 others entries in nommu.c but I guess this is not supported,
> isn't it?

Yes, PER_VMA_LOCK config depends on MMU but for completeness we could
add locking there as well (it will be compiled out).

>
>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> >  mm/mmap.c  | 2 ++
> >  mm/nommu.c | 2 ++
> >  2 files changed, 4 insertions(+)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 094678b4434b..b0d78bdc0de0 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -421,12 +421,14 @@ static inline void vma_rb_insert(struct vm_area_s=
truct *vma,
> >
> >  static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root =
*root)
> >  {
> > +     vma_mark_locked(vma);
> >       /*
> >        * Note rb_erase_augmented is a fairly large inline function,
> >        * so make sure we instantiate it only once with our desired
> >        * augmented rbtree callbacks.
> >        */
> >       rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
> > +     RB_CLEAR_NODE(&vma->vm_rb);
> >  }
> >
> >  static __always_inline void vma_rb_erase_ignore(struct vm_area_struct =
*vma,
> > diff --git a/mm/nommu.c b/mm/nommu.c
> > index e819cbc21b39..ff9933e57501 100644
> > --- a/mm/nommu.c
> > +++ b/mm/nommu.c
> > @@ -622,6 +622,7 @@ static void delete_vma_from_mm(struct vm_area_struc=
t *vma)
> >       struct mm_struct *mm =3D vma->vm_mm;
> >       struct task_struct *curr =3D current;
> >
> > +     vma_mark_locked(vma);
> >       mm->map_count--;
> >       for (i =3D 0; i < VMACACHE_SIZE; i++) {
> >               /* if the vma is cached, invalidate the entire cache */
> > @@ -644,6 +645,7 @@ static void delete_vma_from_mm(struct vm_area_struc=
t *vma)
> >
> >       /* remove from the MM's tree and list */
> >       rb_erase(&vma->vm_rb, &mm->mm_rb);
> > +     RB_CLEAR_NODE(&vma->vm_rb);
> >
> >       __vma_unlink_list(mm, vma);
> >  }
>