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[204.195.120.218]) by smtp.gmail.com with ESMTPSA id 17-20020a17090a035100b002009db534d1sm2123080pjf.24.2022.11.16.14.25.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Nov 2022 14:25:50 -0800 (PST) Date: Wed, 16 Nov 2022 14:25:48 -0800 From: Stephen Hemminger <stephen@networkplumber.org> To: Luc Pelletier <lucp.at.work@gmail.com> Cc: Konstantin Ananyev <konstantin.ananyev@huawei.com>, "grive@u256.net" <grive@u256.net>, "dev@dpdk.org" <dev@dpdk.org>, "stable@dpdk.org" <stable@dpdk.org>, hyonkim@cisco.com, johndale@cisco.com Subject: Re: [PATCH] failsafe: fix segfault on hotplug event Message-ID: <20221116142548.554a7a9e@hermes.local> In-Reply-To: <CAFeRdtC_qfkfJc0DVpfZm8k-BcjTR-SfBd102dtqQZAr4voa4Q@mail.gmail.com> References: <20221110163410.12734-1-lucp.at.work@gmail.com> <d212a2d469404e3091099e2ad901eafe@huawei.com> <CAFeRdtC_qfkfJc0DVpfZm8k-BcjTR-SfBd102dtqQZAr4voa4Q@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: patches for DPDK stable branches <stable.dpdk.org> List-Unsubscribe: <https://mails.dpdk.org/options/stable>, <mailto:stable-request@dpdk.org?subject=unsubscribe> List-Archive: <http://mails.dpdk.org/archives/stable/> List-Post: <mailto:stable@dpdk.org> List-Help: <mailto:stable-request@dpdk.org?subject=help> List-Subscribe: <https://mails.dpdk.org/listinfo/stable>, <mailto:stable-request@dpdk.org?subject=subscribe> Errors-To: stable-bounces@dpdk.org On Wed, 16 Nov 2022 16:51:59 -0500 Luc Pelletier <lucp.at.work@gmail.com> wrote: > Hi Konstantin, > > > It is not recommended way to update rte_eth_fp_ops[] contents directly. > > There are eth_dev_fp_ops_setup()/ eth_dev_fp_ops_reset() that supposed > > to be used for that. > > Good to know. I see another fix that was made in a different PMD that > does exactly the same thing: > > https://github.com/DPDK/dpdk/commit/bcd68b68415172815e55fc67cf3947c0433baf74 > > CC'ing the authors for awareness. > > > About the fix itself - while it might help till some extent, > > I think it will not remove the problem completely. > > There still remain a race-condition between rte_eth_rx_burst() and failsafe_eth_rmv_event_callback(). > > Right now DPDK doesn't support switching PMD fast-ops functions (or updating rxq/txq data) > > on the fly. > > Thanks for the information. This is very helpful. > > Are you saying that the previous code also had that same race > condition? It was only updating the rte_eth_dev structure, but I > assume the problem would have been the same since rte_eth_rx_burst() > in DPDK versions <=20 use the function pointers in rte_eth_dev, not > rte_eth_fp_ops. > > Can you think of a possible solution to this problem? I'm happy to > provide a patch to properly fix the problem. Having your guidance > would be extremely helpful. > > Thanks! Changing burst mode on a running device is not safe because of lack of locking and/or memory barriers. Would have been better to not to do this optimization. Just have one rx_burst/tx_burst function and look at what ever conditions are present there.