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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a1b748cbfdsm4389935e9.0.2026.10.13.18.14.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Oct 2026 18:14:17 -0700 (PDT) Message-ID: <86ae9136-3413-45b2-99b0-fbe404ef1b39@gmail.com> Date: Wed, 14 Oct 2026 02:14:16 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] io_uring/cmd_net: prevent infinite retry loop on unextractable timestamp skb To: Bui Viet Dung , Jens Axboe Cc: Willem de Bruijn , lollipopkit , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20b406ac-94ec-4b0f-a307-08082092ae08@gmail.com> <6ac7afc4.cf15ae49.1a8a2a.2a55@mx.google.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <6ac7afc4.cf15ae49.1a8a2a.2a55@mx.google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit n 10/8/26 15:59, Bui Viet Dung wrote: > On Thu, Oct 8, 2026 at 3:43 PM Pavel Begunkov wrote: >> Sounds fine since there are only timestamp skbs in this list, do >> you have a test case? > > Hi Pavel, > > Thanks for the review. > > The issue was spotted during code inspection of the error handling path > in io_uring_cmd_timestamp(): specifically when skb_get_tx_timestamp() returns > a negative error (e.g. -ENOENT due to missing PHC bindings with > SOF_TIMESTAMPING_BIND_PHC or unavailable timestamp data). Since the > multishot apoll remains armed on EPOLLERR and the unhandled skb is spliced > back onto the head of sk_error_queue, it immediately re-triggers the command > in a tight busy-loop. > > Below is a standalone test program demonstrating the TX_TIMESTAMP command > setup and execution with CQE32: Did you actually reproduce it? This program doesn't for me, nor does fault injection. Taking a look at the code, io_uring_cmd_timestamp() returns -EAGAIN, and the request will wait for the next wake up in the polling code. There are bits to improve, but that's not an infinite loop. -- Pavel Begunkov