dm pcache: fix cache info indexing

The on-media cache_info index used sizeof(struct) instead of the
4K metadata stride, so gc_percent updates from dmsetup message
were written between slots and lost after reboot. Use
PCACHE_CACHE_INFO_SIZE in get_cache_info_addr() and align
info_index with the slot returned by pcache_meta_find_latest().

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
Signed-off-by: Dongsheng Yang <dongsheng.yang@linux.dev>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Zheng Gu <cengku@gmail.com>
Cc: stable@vger.kernel.org	# 6.18

Author: FirstLoveLife

drivers/md/dm-pcache/cache.c

@@ -10,7 +10,8 @@ struct kmem_cache *key_cache;
 
 static inline struct pcache_cache_info *get_cache_info_addr(struct pcache_cache *cache)
 {
-	return cache->cache_info_addr + cache->info_index;
+	return (struct pcache_cache_info *)((char *)cache->cache_info_addr +
+						(size_t)cache->info_index * PCACHE_CACHE_INFO_SIZE);
 }
 
 static void cache_info_write(struct pcache_cache *cache)
@@ -49,6 +50,8 @@ static int cache_info_init(struct pcache_cache *cache, struct pcache_cache_optio
 			return -EINVAL;
 		}
 
+		cache->info_index = ((char *)cache_info_addr - (char *)cache->cache_info_addr) / PCACHE_CACHE_INFO_SIZE;
+
 		return 0;
 	}