Commit 097d70c6 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Andrew Morton
Browse files

mm/mmap/vma_merge: use the proper vma pointer in case 3 

In case 3 we we use 'next' for everything but vma_pgoff.  So use 'next'
for that as well, instead of 'mid', for consistency.  Then in case 8 we
have to use 'mid' explicitly, which should also make the intent more
obvious.

Adjust the diagram for cases 1-3 in the comment to match the code - we are
using 'next' for case 3 so mark the range with XXXX instead of NNNN.  For
case 2 that's a no-op as the code doesn't touch 'next' or 'mid'.  For case
1 it's now wrong but that will be fixed next.

No functional change.

Link: https://lkml.kernel.org/r/20230309111258.24079-3-vbabka@suse.cz


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarLorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: default avatarLiam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 50dac011

mm/mmap.c

+5 −4
Original line number Diff line number Diff line
@@ -857,11 +857,11 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags, 
 *    mmap, brk or    case 4 below       case 5 below

 *    mremap move:

 *                        AAAA               AAAA

 *                    PPPP    NNNN       PPPPNNNNXXXX

 *                    PPPP    XXXX       PPPPNNNNXXXX

 *                    might become       might become

 *                    PPPPPPPPPPPP 1 or  PPPPPPPPPPPP 6 or

 *                    PPPPPPPPNNNN 2 or  PPPPPPPPXXXX 7 or

 *                    PPPPNNNNNNNN 3     PPPPXXXXXXXX 8

 *                    PPPPPPPPXXXX 2 or  PPPPPPPPXXXX 7 or

 *                    PPPPXXXXXXXX 3     PPPPXXXXXXXX 8

 *

 * It is important for case 8 that the vma NNNN overlapping the

 * region AAAA is never going to extended over XXXX. Instead XXXX must
@@ -978,9 +978,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 
			vma = next;			/* case 3 */

			vma_start = addr;

			vma_end = next->vm_end;

			vma_pgoff = mid->vm_pgoff;

			vma_pgoff = next->vm_pgoff;

			err = 0;

			if (mid != next) {		/* case 8 */

				vma_pgoff = mid->vm_pgoff;

				remove = mid;

				err = dup_anon_vma(next, mid);

			}