Re: [PATCH 2/3] dm pcache: fix cache info indexing

[Mikulas Patocka]

On Thu, 4 Dec 2025, Dongsheng Yang wrote:

> From: Li Chen <chenl...@chinatelecom.cn>
> 
> 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 <chenl...@chinatelecom.cn>
> Signed-off-by: Dongsheng Yang <dongsheng.y...@linux.dev>
> ---
>  drivers/md/dm-pcache/cache.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm-pcache/cache.c b/drivers/md/dm-pcache/cache.c
> index 9289c016b7c9..bcc4e509aa69 100644
> --- a/drivers/md/dm-pcache/cache.c
> +++ b/drivers/md/dm-pcache/cache.c
> @@ -8,9 +8,11 @@
>  
>  struct kmem_cache *key_cache;
>  
> -static inline struct pcache_cache_info *get_cache_info_addr(struct 
> pcache_cache *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 +51,8 @@ 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;
>       }
>  
> -- 
> 2.43.0

I already staged the patch below? Should I revert it and stage your new 
patch?

Mikulas


diff --git a/drivers/md/dm-pcache/cache.c b/drivers/md/dm-pcache/cache.c
index d8e92367d947..9554d1158450 100644
--- a/drivers/md/dm-pcache/cache.c
+++ b/drivers/md/dm-pcache/cache.c
@@ -8,9 +8,11 @@

 struct kmem_cache *key_cache;

-static inline struct pcache_cache_info *get_cache_info_addr(struct 
pcache_cache *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)
@@ -40,7 +42,12 @@ static int cache_info_init(struct pcache_cache *cache, 
struct pcache_cache_optio
        if (IS_ERR(cache_info_addr))
                return PTR_ERR(cache_info_addr);

-       if (cache_info_addr) {
+    if (cache_info_addr) {
+               int index = ((char *)cache_info_addr - (char 
*)cache->cache_info_addr) /
+                               PCACHE_CACHE_INFO_SIZE;
+
+               cache->info_index = (index + 1) % PCACHE_META_INDEX_MAX;
+
                if (opts->data_crc !=
                                (cache->cache_info.flags & 
PCACHE_CACHE_FLAGS_DATA_CRC)) {
                        pcache_dev_err(pcache, "invalid option for data_crc: 
%s, expected: %s",