linux-kernel - Re: [PATCH 1/2] dm pcache: fix cache info indexing

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Message-ID: <3222d76f-3710-4238-b90e-cd1deb0d0912@linux.dev>
Date: Wed, 3 Dec 2025 13:56:33 +0800
From: Dongsheng Yang <dongsheng.yang@...ux.dev>
To: Li Chen <me@...ux.beauty>, dm-devel@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Zheng Gu <cengku@...il.com>
Subject: Re: [PATCH 1/2] dm pcache: fix cache info indexing


在 12/2/2025 8:11 PM, Li Chen 写道:
> From: Li Chen <chenl311@...natelecom.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 <chenl311@...natelecom.cn>
> ---
>   drivers/md/dm-pcache/cache.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/dm-pcache/cache.c b/drivers/md/dm-pcache/cache.c
> index 698697a7a73c..6d5001548628 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) {


this is unrelated change, and it introduce error in checkpatch.pl

# ./scripts/checkpatch.pl drivers/md/dm-pcache/cache.c
WARNING: please, no spaces at the start of a line
#45: FILE: drivers/md/dm-pcache/cache.c:45:
+    if (cache_info_addr) {$

WARNING: suspect code indent for conditional statements (4, 16)
#45: FILE: drivers/md/dm-pcache/cache.c:45:
+    if (cache_info_addr) {
+               int index = ((char *)cache_info_addr - (char 
*)cache->cache_info_addr) /

total: 0 errors, 2 warnings, 452 lines checked

> +		int index = ((char *)cache_info_addr - (char *)cache->cache_info_addr) /
> +				PCACHE_CACHE_INFO_SIZE;
> +
> +		cache->info_index = (index + 1) % PCACHE_META_INDEX_MAX;


Don't advance info_index at init stage, cache->info_index means the 
current index, not the next index.

It will be advanced in cache_info_write() after write cache_info into 
next slot.

In addition, cache->info_index initialization should be after the 
data_crc checking.

Thanx

> +
>   		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",