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

From: Stephen Rothwell <[email-masked]>
Date: Fri, 28 Jul 2023 09:18:49 +1000

Hi all,

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) {