Re: [PATCH net-next v10 4/4] page_pool: skip dma sync operation for inflight pages

[Jason Gunthorpe]

On Wed, Feb 26, 2025 at 07:03:39PM +0800, Yunsheng Lin wrote:
> Skip dma sync operation for inflight pages before the
> sync operation in page_pool_item_unmap() as DMA API
> expects to be called with a valid device bound to a
> driver as mentioned in [1].
> 
> After page_pool_destroy() is called, the page is not
> expected to be recycled back to pool->alloc cache and
> dma sync operation is not needed when the page is not
> recyclable or pool->ring is full, so only skip the dma
> sync operation for the infilght pages by clearing the
> pool->dma_sync, as rcu sync operation in
> page_pool_destroy() is paired with rcu lock in
> page_pool_recycle_in_ring() to ensure that there is no
> dma sync operation called after rcu sync operation.

Are you guaranteeing that the cache is made consistent before freeing
the page back to the mm? That is required..

Jason