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

From: Matthew Wilcox <[email-masked]>
Date: Fri, 28 Jul 2023 00:50:29 +0100

On Thu, Jul 27, 2023 at 04:40:20PM -0700, Suren Baghdasaryan wrote:
> On Thu, Jul 27, 2023 at 4:29 PM Stephen Rothwell <[email-masked]> wrote:
> >
> > Hi all,
> >
> > On Fri, 28 Jul 2023 09:18:49 +1000 Stephen Rothwell <[email-masked]> 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)))
> 
> Is the above extra '+' what compiler complains about?
> Patches from Linus' tree remove some code from that function, so
> applying them first should simplify the merge.

I see you're unfamiliar with the output of git diff --cc ...