mm: memcg: factor out trylock_stock() and unlock_stock()

mm: memcg: factor out trylock_stock() and unlock_stock()

Patch series "memcg: obj stock and slab stat caching cleanups".

This is a follow-up to `[PATCH] memcg: fix slab accounting in
refill_obj_stock() trylock path`.  The way the slab stat cache and the
objcg charge cache interact appears a bit too fragile.  This series
factors those paths apart as much as practical.

This patch (of 5):

Consolidate the local lock acquisition and the local stock lookup.  This
allows subsequent patches to use !!stock as an easy way to disambiguate
the locked vs.  contended cases through the callstack.

Link: https://lkml.kernel.org/r/20260302195305.620713-1-hannes@cmpxchg.org
Link: https://lkml.kernel.org/r/20260302195305.620713-2-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Hao Li <hao.li@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>