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([2601:282:800:fd80:950d:299e:8124:b280]) by smtp.googlemail.com with ESMTPSA id m131sm984427pfc.25.2019.05.01.07.52.40 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 May 2019 07:52:41 -0700 (PDT) Subject: Re: unregister_netdevice: waiting for DEV to become free (2) To: Tetsuo Handa , Eric Dumazet , "David S. Miller" Cc: Julian Anastasov , Cong Wang , syzbot , ddstreet@ieee.org, dvyukov@google.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <0000000000007d22100573d66078@google.com> <4684eef5-ea50-2965-86a0-492b8b1e4f52@I-love.SAKURA.ne.jp> <9d430543-33c3-0d9b-dc77-3a179a8e3919@I-love.SAKURA.ne.jp> <920ebaf1-ee87-0dbb-6805-660c1cbce3d0@I-love.SAKURA.ne.jp> <15b353e9-49a2-f08b-dc45-2e9bad3abfe2@i-love.sakura.ne.jp> <057735f0-4475-7a7b-815f-034b1095fa6c@gmail.com> <6e57bc11-1603-0898-dfd4-0f091901b422@i-love.sakura.ne.jp> <117fcc49-d389-c389-918f-86ccaef82e51@i-love.sakura.ne.jp> From: David Ahern Message-ID: <70be7d61-a6fe-e703-978a-d17f544efb44@gmail.com> Date: Wed, 1 May 2019 08:52:37 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <117fcc49-d389-c389-918f-86ccaef82e51@i-love.sakura.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/1/19 7:38 AM, Tetsuo Handa wrote: > On 2019/04/30 3:43, David Ahern wrote: >>> The attached patch adds a tracepoint to notifier_call_chain. If you have >>> KALLSYMS enabled it will show the order of the function handlers: >>> >>> perf record -e notifier:* -a -g & >>> >>> ip netns del >>> >>> >>> fg >>> >>> >>> perf script >>> >> >> with the header file this time. >> > > What is the intent of your patch? I can see that many notifiers are called. But > how does this help identify which event is responsible for dropping the refcount? > In a previous response you stated: "Since I'm not a netdev person, I appreciate if you can explain that shutdown sequence using a flow chart." The notifier sequence tells you the order of cleanup handlers and what happens when a namespace is destroyed. The dev_hold / dev_put tracepoint helps find the refcnt leak but requires some time analyzing the output to match up hold / put stack traces.