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Message-ID: <70be7d61-a6fe-e703-978a-d17f544efb44@gmail.com> Date: Wed, 1 May 2019 08:52:37 -0600 From: David Ahern <dsahern@...il.com> To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Eric Dumazet <eric.dumazet@...il.com>, "David S. Miller" <davem@...emloft.net> Cc: Julian Anastasov <ja@....bg>, Cong Wang <xiyou.wangcong@...il.com>, syzbot <syzbot+30209ea299c09d8785c9@...kaller.appspotmail.com>, ddstreet@...e.org, dvyukov@...gle.com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com Subject: Re: unregister_netdevice: waiting for DEV to become free (2) 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 <NAME> >>> <wait a few seconds> >>> >>> fg >>> <ctrl-c on perf-record> >>> >>> 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.
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