netdev - Re: unregister_netdevice: waiting for DEV to become free (2)

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Date:   Mon, 15 Apr 2019 09:35:01 -0600
From:   David Ahern <dsahern@...il.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Julian Anastasov <ja@....bg>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     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 4/15/19 7:36 AM, Tetsuo Handa wrote:
> I traced using debug printk() patch shown below.
> 

I find tracepoints (see attached patch) and perf are easier to use to
debug device refcnt problems.

For example, limit the stack you have to deal with via sysctl -w
kernel.perf_event_max_stack=16, and add a filter (e.g., --filter 'name
== "lo"') to limit collection to a specific device.

View attachment "0001-Add-tracepoints-to-dev_hold-and-dev_put.patch" of type "text/plain" (2875 bytes)