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

[Mikulas Patocka]

On Thu, 4 Dec 2025, Dongsheng Yang wrote:

> From: Li Chen <chenl...@chinatelecom.cn>
> 
> Segment info indexing also used sizeof(struct) instead of the
> 4K metadata stride, so info_index could point between slots and
> subsequent writes would advance incorrectly. Derive info_index
> from the pointer returned by the segment meta search using
> PCACHE_SEG_INFO_SIZE and advance to the next slot for future
> updates.
> 
> Signed-off-by: Li Chen <chenl...@chinatelecom.cn>
> Signed-off-by: Dongsheng Yang <dongsheng.y...@linux.dev>
> ---
>  drivers/md/dm-pcache/cache_segment.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-pcache/cache_segment.c 
> b/drivers/md/dm-pcache/cache_segment.c
> index ae57cc261422..9d92e2b067ed 100644
> --- a/drivers/md/dm-pcache/cache_segment.c
> +++ b/drivers/md/dm-pcache/cache_segment.c
> @@ -56,7 +56,10 @@ static int cache_seg_info_load(struct pcache_cache_segment 
> *cache_seg)
>               ret = -EIO;
>               goto out;
>       }
> -     cache_seg->info_index = cache_seg_info_addr - cache_seg_info_addr_base;
> +
> +     cache_seg->info_index =
> +             ((char *)cache_seg_info_addr - (char 
> *)cache_seg_info_addr_base) /
> +             PCACHE_SEG_INFO_SIZE;
>  out:
>       mutex_unlock(&cache_seg->info_lock);
>  

Hi

I already staged the patch below. Which patch is valid? Your new patch or 
the patch that I staged?

Mikulas



diff --git a/drivers/md/dm-pcache/cache_segment.c 
b/drivers/md/dm-pcache/cache_segment.c
index f0b58980806e..0b4bb08011ce 100644
--- a/drivers/md/dm-pcache/cache_segment.c
+++ b/drivers/md/dm-pcache/cache_segment.c
@@ -56,7 +56,11 @@ static int cache_seg_info_load(struct 
pcache_cache_segment *cache_seg)
                ret = -EIO;
                goto out;
        }
-       cache_seg->info_index = cache_seg_info_addr - cache_seg_info_addr_base;
+
+       cache_seg->info_index =
+               ((char *)cache_seg_info_addr - (char 
*)cache_seg_info_addr_base) /
+               PCACHE_SEG_INFO_SIZE;
+       cache_seg->info_index = (cache_seg->info_index + 1) % 
PCACHE_META_INDEX_MAX;
 out:
        mutex_unlock(&cache_seg->info_lock);