mm/memcontrol: fix reclaim_options leak in try_charge_memcg()

mm/memcontrol: fix reclaim_options leak in try_charge_memcg()

In try_charge_memcg(), the 'reclaim_options' variable is initialized once
at the start of the function.  However, the function contains a retry
loop.  If reclaim_options were modified during an iteration (e.g., by
encountering a memsw limit), the modified state would persist into
subsequent retries.

This leads to incorrect reclaim behavior.  Specifically,
MEMCG_RECLAIM_MAY_SWAP is cleared when the combined memcg->memsw limit is
reached.  After reclaimation attempts, a subsequent retry may successfully
charge memcg->memsw but fail on the memcg->memory charge.  In this case,
swapping should be permitted, but the carried-over state prevents it.

This issue was identified during code reading of try_charge_memcg() while
analyzing memsw limit behavior in tiered-memory systems; no production
failures have been reported yet.

Fix by moving the initialization of 'reclaim_options' inside the retry
loop, ensuring a clean state for every reclaim attempt.

Link: https://lkml.kernel.org/r/20260321033500.2558070-1-bingjiao@google.com
Fixes: 6539cc053869 ("mm: memcontrol: fold mem_cgroup_do_charge()")
Signed-off-by: Bing Jiao <bingjiao@google.com>
Reviewed-by: Yosry Ahmed <yosry@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>