nommu: pass NULL argument to vma_iter_prealloc()

nommu: pass NULL argument to vma_iter_prealloc()

When deleting a vma entry from a maple tree, it has to pass NULL to
vma_iter_prealloc() in order to calculate internal state of the tree, but
it passed a wrong argument.  As a result, nommu kernels crashed upon
accessing a vma iterator, such as acct_collect() reading the size of vma
entries after do_munmap().

This commit fixes this issue by passing a right argument to the
preallocation call.

Link: https://lkml.kernel.org/r/20241108222834.3625217-1-thehajime@gmail.com
Fixes: b5df09226450 ("mm: set up vma iterator for vma_iter_prealloc() calls")
Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>