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

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Message-ID: <eede7cda-6621-408f-be86-21c667d7d14f@linux.dev>
Date: Thu, 4 Dec 2025 07:38:51 +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 12/3/2025 1:57 PM, Dongsheng Yang 写道:
>
> 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.


ignore this incorrect comment, info_index means next slot, we need to 
advance it here.

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