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Miller" , Jakub Kicinski , Jesper Dangaard Brouer , Saeed Mahameed , Leon Romanovsky , Tariq Toukan , Andrew Lunn , Eric Dumazet , Paolo Abeni , Ilias Apalodimas , Simon Horman , Andrew Morton , Mina Almasry , Yonglong Liu , Yunsheng Lin , Pavel Begunkov , Matthew Wilcox , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, Qiuling Ren , Yuying Ma Subject: Re: [PATCH net-next v7 2/2] page_pool: Track DMA-mapped pages and unmap them when destroying the pool In-Reply-To: References: <20250404-page-pool-track-dma-v7-0-ad34f069bc18@redhat.com> <20250404-page-pool-track-dma-v7-2-ad34f069bc18@redhat.com> <3b933890-7ff2-4aaf-aea5-06e5889ca087@intel.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Sat, 05 Apr 2025 14:50:00 +0200 Message-ID: <87jz7yhix3.fsf@toke.dk> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Alexander Lobakin writes: > From: Alexander Lobakin > Date: Fri, 4 Apr 2025 17:55:43 +0200 > >> From: Toke H=C3=B8iland-J=C3=B8rgensen >> Date: Fri, 04 Apr 2025 12:18:36 +0200 >>=20 >>> 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. >>=20 >> [...] >>=20 >>> -#define PP_MAGIC_MASK ~0x3UL >>> +#define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL) >>>=20=20 >>> /** >>> * struct page_pool_params - page pool parameters >>> @@ -173,10 +212,10 @@ struct page_pool { >>> int cpuid; >>> u32 pages_state_hold_cnt; >>>=20=20 >>> - bool has_init_callback:1; /* slow::init_callback is set */ >>> + bool dma_sync; /* Perform DMA sync for device */ >>=20 >> Yunsheng said this change to a full bool is redundant in the v6 thread >> =C2=AF\_(=E3=83=84)_/=C2=AF AFAIU, the comment was that the second READ_ONCE() when reading the field was redundant, because of the rcu_read_lock(). Which may be the case, but I think keeping it makes the intent of the code clearer. And in any case, it has nothing to do with changing the type of the field... -Toke