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Date: Sun, 16 Jul 2023 16:57:07 -0700
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Subject: Re: [RFC PATCH 06/10] net: add SO_DEVMEM_DONTNEED setsockopt to
 release RX pages
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To: Mina Almasry <almasrymina@google.com>, linux-kernel@vger.kernel.org,
 linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
 linaro-mm-sig@lists.linaro.org, netdev@vger.kernel.org,
 linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org
Cc: Sumit Semwal <sumit.semwal@linaro.org>,
 =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
 "David S. Miller" <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>,
 Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
 Jesper Dangaard Brouer <hawk@kernel.org>,
 Ilias Apalodimas <ilias.apalodimas@linaro.org>, Arnd Bergmann
 <arnd@arndb.de>, David Ahern <dsahern@kernel.org>,
 Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
 Shuah Khan <shuah@kernel.org>, jgg@ziepe.ca
References: <20230710223304.1174642-1-almasrymina@google.com>
 <20230710223304.1174642-7-almasrymina@google.com>
From: Andy Lutomirski <luto@kernel.org>
In-Reply-To: <20230710223304.1174642-7-almasrymina@google.com>
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On 7/10/23 15:32, Mina Almasry wrote:
> Add an interface for the user to notify the kernel that it is done reading
> the NET_RX dmabuf pages returned as cmsg. The kernel will drop the
> reference on the NET_RX pages to make them available for re-use.
> 
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> ---

> +		for (i = 0; i < num_tokens; i++) {
> +			for (j = 0; j < tokens[i].token_count; j++) {
> +				struct page *pg = xa_erase(&sk->sk_pagepool,
> +							   tokens[i].token_start + j);
> +
> +				if (pg)
> +					put_page(pg);
> +				else
> +					/* -EINTR here notifies the userspace
> +					 * that not all tokens passed to it have
> +					 * been freed.
> +					 */
> +					ret = -EINTR;

Unless I'm missing something, this type of error reporting is 
unrecoverable -- userspace doesn't know how many tokens have been freed.

I think you should either make it explicitly unrecoverable (somehow shut 
down dmabuf handling entirely) or tell userspace how many tokens were 
successfully freed.

--Andy