Re: [PATCH net-next v5 2/2] page_pool: Track DMA-mapped pages and unmap them when destroying the pool

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2025/3/31 18:35, Alexander Lobakin 写道:
> From: Toke Høiland-Jørgensen <toke@redhat.com>
> Date: Fri, 28 Mar 2025 13:19:09 +0100
> 
>> When enabling DMA mapping in page_pool, pages are kept DMA mapped until
>> they are released from the pool, to avoid the overhead of re-mapping the
>> pages every time they are used. This causes resource leaks and/or
>> crashes when there are pages still outstanding while the device is torn
>> down, because page_pool will attempt an unmap through a non-existent DMA
>> device on the subsequent page return.
> 
> [...]
> 
>> @@ -173,10 +212,10 @@ struct page_pool {
>>   	int cpuid;
>>   	u32 pages_state_hold_cnt;
>>   
>> -	bool has_init_callback:1;	/* slow::init_callback is set */
>> +	bool dma_sync;			/* Perform DMA sync for device */
> 
> Have you seen my comment under v3 (sorry but I missed that there was v4
> already)? Can't we just test the bit atomically?

Perhaps test_bit series functions can test the bit atomically. Maybe 
there are more good options about this testing the bit atomically. But 
test_bit should implement the task that tests the bit atomically.

Zhu Yanjun

> 
>>   	bool dma_map:1;			/* Perform DMA mapping */
>> -	bool dma_sync:1;		/* Perform DMA sync for device */
>>   	bool dma_sync_for_cpu:1;	/* Perform DMA sync for cpu */
>> +	bool has_init_callback:1;	/* slow::init_callback is set */
> 
> Thanks,
> Olek