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

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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: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Vlastimil Babka
2023-03-09 12:12:50 +01:00
committed by Andrew Morton
parent 50dac01113
commit 097d70c627
1 changed files with 5 additions and 4 deletions
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9
mm/mmap.c
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@@ -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);
}