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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Thu, 27 Jul 2023 17:08:03 -0700
Message-ID: <CAJuCfpFPyFvaJOWW8NcvibZ5_QQg7t-GOo_270wRBXs8zX7QOg@mail.gmail.com>
Subject: Re: linux-next: manual merge of the mm tree with Linus' tree
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jann Horn <jannh@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>
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On Thu, Jul 27, 2023 at 4:50=E2=80=AFPM Matthew Wilcox <willy@infradead.org=
> wrote:
>
> On Thu, Jul 27, 2023 at 04:40:20PM -0700, Suren Baghdasaryan wrote:
> > On Thu, Jul 27, 2023 at 4:29=E2=80=AFPM Stephen Rothwell <sfr@canb.auug=
.org.au> wrote:
> > >
> > > Hi all,
> > >
> > > On Fri, 28 Jul 2023 09:18:49 +1000 Stephen Rothwell <sfr@canb.auug.or=
g.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 w=
ant
> > > > 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 l=
ocked */
> > > >  -    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 l=
ocked.
> > > >  +     * 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 ...

guilty as charged.

>