nommu: fix split_vma() map_count error

During the maple tree conversion of nommu, an error in counting the VMAs
was introduced by counting the existing VMA again.  The counting used to
be decremented by one and incremented by two, but now it only increments
by two.  Fix the counting error by moving the increment outside the
setup_vma_to_mm() function to the callers.

Link: https://lkml.kernel.org/r/20230109205809.956325-1-Liam.Howlett@oracle.com
Fixes: 8220543df148 ("nommu: remove uses of VMA linked list")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/nommu.c b/mm/nommu.c
index 844af5be76400b7501868ec50ba1dc588889e4a6..5b83938ecb67cf4533c4a30e997cea3e3111b285 100644 (file)
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -559,7 +559,6 @@ void vma_mas_remove(struct vm_area_struct *vma, struct ma_state *mas)
 
 static void setup_vma_to_mm(struct vm_area_struct *vma, struct mm_struct *mm)
 {
-       mm->map_count++;
        vma->vm_mm = mm;
 
        /* add the VMA to the mapping */
@@ -587,6 +586,7 @@ static void mas_add_vma_to_mm(struct ma_state *mas, struct mm_struct *mm,
        BUG_ON(!vma->vm_region);
 
        setup_vma_to_mm(vma, mm);
+       mm->map_count++;
 
        /* add the VMA to the tree */
        vma_mas_store(vma, mas);
@@ -1347,6 +1347,7 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
        if (vma->vm_file)
                return -ENOMEM;
 
+       mm = vma->vm_mm;
        if (mm->map_count >= sysctl_max_map_count)
                return -ENOMEM;
 
@@ -1398,6 +1399,7 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
        mas_set_range(&mas, vma->vm_start, vma->vm_end - 1);
        mas_store(&mas, vma);
        vma_mas_store(new, &mas);
+       mm->map_count++;
        return 0;
 
 err_mas_preallocate: