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 <[e-mail]>
Signed-off-by: Dongsheng Yang <[e-mail]>
Signed-off-by: Mikulas Patocka <[e-mail]>
Reviewed-by: Zheng Gu <[e-mail]>
Cc: [e-mail] # 6.18

drivers/md/dm-pcache/cache.c

···
 
 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)
···
 					cache->cache_info.flags & PCACHE_CACHE_FLAGS_DATA_CRC ? "true" : "false");
 			return -EINVAL;
 		}
+
+		cache->info_index = ((char *)cache_info_addr - (char *)cache->cache_info_addr) / PCACHE_CACHE_INFO_SIZE;
 
 		return 0;
 	}