mm/mremap: use vma_find_intersection() instead of vma linked list

Using the vma_find_intersection() call allows for cleaner code and
removes linked list users in preparation of the linked list removal.

Also remove one user of the linked list at the same time in favour of
find_vma().

Link: https://lkml.kernel.org/r/20220906194824.2110408-60-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Tested-by: Yu Zhao <yuzhao@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mremap.c

@@ -716,7 +716,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	if (excess) {
 		vma->vm_flags |= VM_ACCOUNT;
 		if (split)
-			vma->vm_next->vm_flags |= VM_ACCOUNT;
+			find_vma(mm, vma->vm_end)->vm_flags |= VM_ACCOUNT;
 	}
 
 	return new_addr;
@@ -866,9 +866,10 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 {
 	unsigned long end = vma->vm_end + delta;
+
 	if (end < vma->vm_end) /* overflow */
 		return 0;
-	if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
+	if (find_vma_intersection(vma->vm_mm, vma->vm_end, end))
 		return 0;
 	if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 			      0, MAP_FIXED) & ~PAGE_MASK)