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[81.170.137.65]) by smtp.gmail.com with ESMTPSA id m2sm2574458ljc.58.2020.07.01.23.14.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 01 Jul 2020 23:14:37 -0700 (PDT) Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc To: Cong Wang , Josh Hunt Cc: Paolo Abeni , Michael Zhivich , David Miller , John Fastabend , LKML , Linux Kernel Network Developers References: <465a540e-5296-32e7-f6a6-79942dfe2618@netrounds.com> <20200623134259.8197-1-mzhivich@akamai.com> <1849b74f-163c-8cfa-baa5-f653159fefd4@akamai.com> From: Jonas Bonn Message-ID: <7fd86d97-6785-0b5f-1e95-92bc1da9df35@netrounds.com> Date: Thu, 2 Jul 2020 08:14:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi Cong, On 01/07/2020 21:58, Cong Wang wrote: > On Wed, Jul 1, 2020 at 9:05 AM Cong Wang wrote: >> >> On Tue, Jun 30, 2020 at 2:08 PM Josh Hunt wrote: >>> Do either of you know if there's been any development on a fix for this >>> issue? If not we can propose something. >> >> If you have a reproducer, I can look into this. > > Does the attached patch fix this bug completely? It's easier to comment if you inline the patch, but after taking a quick look it seems too simplistic. i) Are you sure you haven't got the return values on qdisc_run reversed? ii) There's a "bypass" path that skips the enqueue/dequeue operation if the queue is empty; that needs a similar treatment: after releasing seqlock it needs to ensure that another packet hasn't been enqueued since it last checked. /Jonas > > Thanks. >