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

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Message-ID: <8794c32c-790c-4503-a657-3e66bc541cda@linux.dev>
Date: Wed, 3 Dec 2025 13:57:15 +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 2/2] dm pcache: fix segment info indexing


在 12/2/2025 8:11 PM, Li Chen 写道:
> From: Li Chen <chenl311@...natelecom.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 <chenl311@...natelecom.cn>
> ---
>   drivers/md/dm-pcache/cache_segment.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> 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;


Don't advance info_index at init stage.

>   out:
>   	mutex_unlock(&cache_seg->info_lock);
>