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Date:   Mon, 15 Apr 2019 09:35:01 -0600
From:   David Ahern <>
To:     Tetsuo Handa <>,
        Julian Anastasov <>,
        Cong Wang <>
Cc:     syzbot <>,,,,,
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)

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