mm: fix unaccount of memory on vma_link() failure

Fix insert_vm_struct() so that only accounted memory is unaccounted if
vma_link() fails.

Link: https://lkml.kernel.org/r/20230830004324.16101-1-anthony.yznaga@oracle.com
Fixes: d4af56c5 ("mm: start tracking VMAs with maple tree")
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c

@@ -3278,7 +3278,8 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 	}
 
 	if (vma_link(mm, vma)) {
-		vm_unacct_memory(charged);
+		if (vma->vm_flags & VM_ACCOUNT)
+			vm_unacct_memory(charged);
 		return -ENOMEM;
 	}