Re: linux-next: manual merge of the mm tree with Linus' tree

Stephen Rothwell
2023-07-28T00:00:54Z

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Hi all,

On Fri, 28 Jul 2023 09:29:15 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>
> On Fri, 28 Jul 2023 09:18:49 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> >
> > Today's linux-next merge of the mm tree got a conflict in:
> >
> > mm/memory.c
> >
> > between commit:
> >
> > 657b5146955e ("mm: lock_vma_under_rcu() must check vma->anon_vma under vma lock")
> >
> > from Linus' tree and commits:
> >
> > 69f6bbd1317f ("mm: handle userfaults under VMA lock")
> > a3bdf38e85aa ("mm: allow per-VMA locks on file-backed VMAs")
> >
> > from the mm tree.
> >
> > I fixed it up (I think, please check - see below) and can carry the fix
> > as necessary. This is now fixed as far as linux-next is concerned, but
> > any non trivial conflicts should be mentioned to your upstream
> > maintainer when your tree is submitted for merging. You may also want
> > to consider cooperating with the maintainer of the conflicting tree to
> > minimise any particularly complex conflicts.
> >
> > --
> > Cheers,
> > Stephen Rothwell
> >
> > diff --cc mm/memory.c
> > index ca632b58f792,271982fab2b8..000000000000
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@@ -5392,32 -5597,18 +5597,21 @@@ retry
> > if (!vma)
> > goto inval;
> >
> > - /* Only anonymous and tcp vmas are supported for now */
> > - if (!vma_is_anonymous(vma) && !vma_is_tcp(vma))
> > - /* find_mergeable_anon_vma uses adjacent vmas which are not locked */
> > - if (vma_is_anonymous(vma) && !vma->anon_vma)
> > -- goto inval;
> > --
> > if (!vma_start_read(vma))
> > goto inval;
> >
> > + /*
> > + * find_mergeable_anon_vma uses adjacent vmas which are not locked.
> > + * This check must happen after vma_start_read(); otherwise, a
> > + * concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA
> > + * from its anon_vma.
> > + */
> > - if (unlikely(!vma->anon_vma && !vma_is_tcp(vma)))
> > - goto inval_end_read;
> > -
> > - /*
> > - * Due to the possibility of userfault handler dropping mmap_lock, avoid
> > - * it for now and fall back to page fault handling under mmap_lock.
> > - */
> > - if (userfaultfd_armed(vma))
> > ++ if (unlikely(vma_is_anonymous(vma) && !vma_is_tcp(vma)))
> > + goto inval_end_read;
> > +
> > /* Check since vm_start/vm_end might change before we lock the VMA */
> > - if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
> > - vma_end_read(vma);
> > - goto inval;
> > - }
> > + if (unlikely(address < vma->vm_start || address >= vma->vm_end))
> > + goto inval_end_read;
> >
> > /* Check if the VMA got isolated after we found it */
> > if (vma->detached) {
>
> Sorry, doesn't even build ... let me try that again.

I have gone with below. Again, please check.

--
Cheers,
Stephen Rothwell

diff --cc mm/memory.c
index ca632b58f792,271982fab2b8..000000000000
--- a/mm/memory.c
+++ b/mm/memory.c
@@@ -5392,32 -5597,18 +5597,21 @@@ retry
if (!vma)
goto inval;

- /* Only anonymous and tcp vmas are supported for now */
- if (!vma_is_anonymous(vma) && !vma_is_tcp(vma))
- /* find_mergeable_anon_vma uses adjacent vmas which are not locked */
- if (vma_is_anonymous(vma) && !vma->anon_vma)
-- goto inval;
--
if (!vma_start_read(vma))
goto inval;

+ /*
+ * find_mergeable_anon_vma uses adjacent vmas which are not locked.
+ * This check must happen after vma_start_read(); otherwise, a
+ * concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA
+ * from its anon_vma.
+ */
- if (unlikely(!vma->anon_vma && !vma_is_tcp(vma)))
- goto inval_end_read;
-
- /*
- * Due to the possibility of userfault handler dropping mmap_lock, avoid
- * it for now and fall back to page fault handling under mmap_lock.
- */
- if (userfaultfd_armed(vma))
++ if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma))
+ goto inval_end_read;
+
/* Check since vm_start/vm_end might change before we lock the VMA */
- if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
- vma_end_read(vma);
- goto inval;
- }
+ if (unlikely(address < vma->vm_start || address >= vma->vm_end))
+ goto inval_end_read;

/* Check if the VMA got isolated after we found it */
if (vma->detached) {

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