mm/mglru: make memcg_lru->lock irq safe

lru_gen_rotate_memcg() can happen in softirq if memory.soft_limit_in_bytes
is set.  This requires memcg_lru->lock to be irq safe.  Lockdep warns on
this.

This problem only affects memcg v1.

Link: https://lkml.kernel.org/r/20230619193821.2710944-1-yuzhao@google.com
Fixes: e4dde56c

 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by:  <syzbot+87c490fd2be656269b6a@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=87c490fd2be656269b6a


Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>