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Mon, 24 Feb 2025 08:00:05 -0800 (PST) Received: from localhost ([2601:646:9e00:f56e:123b:cea3:439a:b3e3]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-220d545d016sm179712775ad.146.2025.02.24.08.00.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2025 08:00:05 -0800 (PST) Date: Mon, 24 Feb 2025 08:00:04 -0800 From: Stanislav Fomichev To: Magnus Karlsson Cc: Wang Liang , bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, yuehaibing@huawei.com, zhangchangzhong@huawei.com, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] xsk: fix __xsk_generic_xmit() error code when cq is full Message-ID: References: <20250222093007.3607691-1-wangliang74@huawei.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 02/24, Magnus Karlsson wrote: > On Sat, 22 Feb 2025 at 10:18, Wang Liang wrote: > > > > When the cq reservation is failed, the error code is not set which is > > initialized to zero in __xsk_generic_xmit(). That means the packet is not > > send successfully but sendto() return ok. > > > > Set the error code and make xskq_prod_reserve_addr()/xskq_prod_reserve() > > return values more meaningful when the queue is full. > > Hi Wang, > > I agree that this would have been a really good idea if it was > implemented from day one, but now I do not dare to change this since > it would be changing the uapi. Let us say you have the following quite > common code snippet for sending a packet with AF_XDP in skb mode: > > err = sendmsg(); > if (err && err != -EAGAIN && err != -EBUSY) > goto die_due_to_error; > continue with code > > This code would with your change go and die suddenly when the > completion ring is full instead of working. Maybe there is a piece of > code that cleans the completion ring after these lines of code and > next time sendmsg() is called, the packet will get sent, so the > application used to work. > > So I say: let us not do this. But if anyone has another opinion, please share. Can we return -EBUSY from this 'if (xsk_cq_reserve_addr_locked())' case as well?