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Date: Sun, 28 Apr 2019 08:04:18 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, David Ahern <dsahern@...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 4/27/19 9:22 PM, Tetsuo Handa wrote: > On 2019/04/28 8:52, Eric Dumazet wrote: >> On 4/27/19 3:33 PM, Tetsuo Handa wrote: >>> >>> I'm waiting for davem why it is safe to move the dst entry from >>> "a device to unregister" to "a loopback device in that namespace". >>> I'm waiting for an explanation how the dst entry which was moved to >>> "a loopback device in that namespace" is released (i.e. what the >>> expected shutdown sequence is). >> >> The most probable explanation is that we make sure the loopback device >> is the last one to be dismantled at netns deletion, >> and this would obviously happen after all dst have been released. >> > > rt_flush_dev() becomes a no-op if "dev" == "a loopback device in that > namespace". And according to debug printk(), rt_flush_dev() is called > on "a loopback device in that namespace" itself. > This is the design yes. We can not let a dst having a pointer to some garbage memory. (since we are going to free it very soon) dst can be long lived objects. netdev (but loopback) are not. > If "a loopback device in that namespace" is the last "one" (== "a network > device in that namespace" ?), which shutdown sequence should have called > dev_put("a loopback device in that namespace") before unregistration of > "a loopback device in that namespace" starts? You'll have to study all the netdev notifiers to answer this question. They are many of them, and they have a priority to let them run in a given order. > > Since I'm not a netdev person, I appreciate if you can explain > that shutdown sequence using a flow chart. I am a netdev person, but I have no time to explain this at this moment.
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