Messages in this thread | | | Date | Tue, 12 Nov 2019 15:18:19 +0800 | From | Tony Lu <> | Subject | Re: [PATCH] net: remove static inline from dev_put/dev_hold |
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On Mon, Nov 11, 2019 at 08:56:32AM -0800, Stephen Hemminger wrote: > On Mon, 11 Nov 2019 22:05:03 +0800 > Tony Lu <tonylu@linux.alibaba.com> 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. > > > > Signed-off-by: Tony Lu <tonylu@linux.alibaba.com> > > In the past dev_hold/dev_put was in the hot path for several > operations. What is the performance implication of doing this?
From code analysis, there should be a little performance backwards. I don't have the benchmark data for now. I will make a kernel module to take a series of benchmarks for dev_put/dev_hold. Actually there is a plan to take a whole solution for this issue. The benchmarks will be done after this.
Cheers Tony Lu
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