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Date:   Sat, 18 Mar 2017 20:49:43 -0700
From:   Cong Wang <>
To:     Kevin Xu <>
Cc:     David Miller <>,
        Linux Kernel Network Developers <>
Subject: Re: [PATCH net v2] net: Do not hold the reference for the same sk_rx_dst

On Sat, Mar 18, 2017 at 6:48 PM, Kevin Xu <> wrote:
> In some rare cases, inet_sk_rx_dst_set() may be called multiple times
> on the same dst, causing double refcounting. Eventually, it
> prevents net_device to be destroyed. The bug manifested as
> unregister_netdevice: waiting for lo to become free. Usage count = 1
> in the kernel log, preventing new network namespace creation.
> Signed-off-by: Kevin Xu <>

Don't know why you don't follow the discussion on your v1...

It is protected by bh_lock_sock(), so your patch is not needed
at all.

Read net/ipv4/udp.c:

1762 /* For TCP sockets, sk_rx_dst is protected by socket lock
1763  * For UDP, we use xchg() to guard against concurrent changes.
1764  */

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