mm/vmalloc: support non-blocking GFP flags in alloc_vmap_area()

mm/vmalloc: support non-blocking GFP flags in alloc_vmap_area()

alloc_vmap_area() currently assumes that sleeping is allowed during
allocation.  This is not true for callers which pass non-blocking GFP
flags, such as GFP_ATOMIC or GFP_NOWAIT.

This patch adds logic to detect whether the given gfp_mask permits
blocking.  It avoids invoking might_sleep() or falling back to reclaim
path if blocking is not allowed.

This makes alloc_vmap_area() safer for use in non-sleeping contexts, where
previously it could hit unexpected sleeps, trigger warnings.

It is a preparation and adjustment step to later allow both GFP_ATOMIC and
GFP_NOWAIT allocations in this series.

Link: https://lkml.kernel.org/r/20251007122035.56347-4-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>