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[146.241.86.8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4406d5d7a3dsm167207845e9.38.2025.04.22.04.21.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Apr 2025 04:21:23 -0700 (PDT) Message-ID: <4295ec79-035c-4858-9ec4-eb639767d12b@redhat.com> Date: Tue, 22 Apr 2025 13:21:22 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v2 0/5] net_sched: Adapt qdiscs for reentrant enqueue cases To: Cong Wang , Victor Nogueira Cc: netdev@vger.kernel.org, jhs@mojatatu.com, jiri@resnulli.us, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, toke@redhat.com, gerrard.tai@starlabs.sg, pctammela@mojatatu.com References: <20250416102427.3219655-1-victor@mojatatu.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/17/25 9:23 PM, Cong Wang wrote: > On Wed, Apr 16, 2025 at 07:24:22AM -0300, Victor Nogueira wrote: >> As described in Gerrard's report [1], there are cases where netem can >> make the qdisc enqueue callback reentrant. Some qdiscs (drr, hfsc, ets, >> qfq) break whenever the enqueue callback has reentrant behaviour. >> This series addresses these issues by adding extra checks that cater for >> these reentrant corner cases. This series has passed all relevant test >> cases in the TDC suite. >> >> [1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/ >> > > I am wondering why we need to enqueue the duplicate skb before enqueuing > the original skb in netem? IOW, why not just swap them? It's not clear to me what you are suggesting, could you please rephrase and/or expand the above? When duplication packets, I think we will need to call root->enqueue() no matter what, to ensure proper accounting, and that would cause the re-entrancy issue. What I'm missing? Thanks, Paolo