Re: [PATCH net-next 1/2] page_pool: Convert page_pool_recycle_stats to u64_stats_t.

[Paolo Abeni <pabeni@redhat.com>]

On 2/22/25 9:13 AM, Yunsheng Lin wrote:
> On 2025/2/21 19:52, Sebastian Andrzej Siewior wrote:
>> @@ -99,11 +106,19 @@ bool page_pool_get_stats(const struct page_pool *pool,
>>  		const struct page_pool_recycle_stats *pcpu =
>>  			per_cpu_ptr(pool->recycle_stats, cpu);
>>  
>> -		stats->recycle_stats.cached += pcpu->cached;
>> -		stats->recycle_stats.cache_full += pcpu->cache_full;
>> -		stats->recycle_stats.ring += pcpu->ring;
>> -		stats->recycle_stats.ring_full += pcpu->ring_full;
>> -		stats->recycle_stats.released_refcnt += pcpu->released_refcnt;
>> +		do {
>> +			start = u64_stats_fetch_begin(&pcpu->syncp);
>> +			u64_stats_add(&stats->recycle_stats.cached,
>> +				      u64_stats_read(&pcpu->cached));
>> +			u64_stats_add(&stats->recycle_stats.cache_full,
>> +				      u64_stats_read(&pcpu->cache_full));
>> +			u64_stats_add(&stats->recycle_stats.ring,
>> +				      u64_stats_read(&pcpu->ring));
>> +			u64_stats_add(&stats->recycle_stats.ring_full,
>> +				      u64_stats_read(&pcpu->ring_full));
>> +			u64_stats_add(&stats->recycle_stats.released_refcnt,
>> +				      u64_stats_read(&pcpu->released_refcnt));
> 
> It seems the above u64_stats_add() may be called more than one time
> if the below u64_stats_fetch_retry() returns true, which might mean
> the stats is added more than it is needed.
> 
> It seems more correct to me that pool->alloc_stats is read into a
> local varible in the while loop and then do the addition outside
> the while loop?

I also think the above code is incorrect, and local variables to store
the read stats are needed.

/P