init: do_mounts: use kmalloc() for allocations of temporary buffers

init: do_mounts: use kmalloc() for allocations of temporary buffers

Several places in init/do_mounts.c allocate temporary buffers for
filesystem names or options using __get_free_page() or alloc_page().

Usage of alloc_page() APIs is not required there and only creates
unnecessary noise with castings or conversion from struct page to void *.

kmalloc() is a better API for these uses and it also provides better
scalability and more debugging possibilities.

Replace use of __get_free_page() and alloc_page() with kmalloc().

While on it, add a check for -ENOMEM condition in mount_root_generic().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Link: https://patch.msgid.link/20260520-init-v1-1-aaf2ebac5ad9@kernel.org
Reviewed-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>