mm: consistently use current->mm in mm_get_unmapped_area()

mm: consistently use current->mm in mm_get_unmapped_area()

mm_get_unmapped_area() is a wrapper around arch_get_unmapped_area() /
arch_get_unmapped_area_topdown(), both of which search current->mm for
some free space.  Neither take an mm_struct - they implicitly operate on
current->mm.

But the wrapper takes an mm_struct and uses it to decide whether to search
bottom up or top down.  All callers pass in current->mm for this, so
everything is working consistently.  But it feels like an accident waiting
to happen; eventually someone will call that function with a different mm,
expecting to find free space in it, but what gets returned is free space
in the current mm.

So let's simplify by removing the parameter and have the wrapper use
current->mm to decide which end to start at.  Now everything is consistent
and self-documenting.

Link: https://lkml.kernel.org/r/20251003155306.2147572-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>