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Subject: Re: [PATCH] net: remove static inline from dev_put/dev_hold
To:     Tony Lu <tonylu@linux.alibaba.com>, davem@davemloft.net
Cc:     shemminger@osdl.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20191111140502.17541-1-tonylu@linux.alibaba.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <c6230ad9-e859-4bee-dacb-4d7910a3f120@gmail.com>
Date:   Mon, 11 Nov 2019 09:21:58 -0800
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On 11/11/19 6:05 AM, Tony Lu wrote:
> This patch removes static inline from dev_put/dev_hold in order to help
> trace the pcpu_refcnt leak of net_device.
> 
> We have sufferred this kind of issue for several times during
> manipulating NIC between different net namespaces. It prints this
> log in dmesg:
> 
>   unregister_netdevice: waiting for eth0 to become free. Usage count = 1
> 
> However, it is hard to find out who called and leaked refcnt in time. It
> only left the crime scene but few evidence. Once leaked, it is not
> safe to fix it up on the running host. We can't trace dev_put/dev_hold
> directly, for the functions are inlined and used wildly amoung modules.
> And this issue is common, there are tens of patches fix net_device
> refcnt leak for various causes.
> 
> To trace the refcnt manipulating, this patch removes static inline from
> dev_put/dev_hold. We can use handy tools, such as eBPF with kprobe, to
> find out who holds but forgets to put refcnt. This will not be called
> frequently, so the overhead is limited.
>

This looks as a first step.

But I would rather get a full set of scripts/debugging features,
instead of something that most people can not use right now.

Please share the whole thing.