netdev - Re: 3.3.0, 3.4-rc1 reproducible tun Oops

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Message-ID: <20120417020852.GA18875@hostway.ca>
Date:	Mon, 16 Apr 2012 19:08:53 -0700
From:	Simon Kirby <sim@...tway.ca>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	netdev@...r.kernel.org
Subject: Re: 3.3.0, 3.4-rc1 reproducible tun Oops

On Thu, Apr 05, 2012 at 04:41:04AM +0200, Eric Dumazet wrote:

> Hmm, is it happening if you remove the nvidia module ?
> 
> If yes, please try to add slub_debug=FZPU

Finally got annoyed enough at this to bisect it. It doesn't happen every
time and I got a bit confused, but I finally tracked it down to:

1ab5ecb90cb6a3df1476e052f76a6e8f6511cb3d is the first bad commit
commit 1ab5ecb90cb6a3df1476e052f76a6e8f6511cb3d
Author: Stanislav Kinsbursky <skinsbursky@...allels.com>
Date:   Mon Mar 12 02:59:41 2012 +0000

    tun: don't hold network namespace by tun sockets
    
    v3: added previously removed sock_put() to the tun_release() callback, because
    sk_release_kernel() doesn't drop the socket reference.
    
    v2: sk_release_kernel() used for socket release. Dummy tun_release() is
    required for sk_release_kernel() ---> sock_release() ---> sock->ops->release()
    call.
    
    TUN was designed to destroy it's socket on network namesapce shutdown. But this
    will never happen for persistent device, because it's socket holds network
    namespace.
    This patch removes of holding network namespace by TUN socket and replaces it
    by creating socket in init_net and then changing it's net it to desired one. On
    shutdown socket is moved back to init_net prior to final put.
    
    Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

...With this reverted on top of 3.4-rc3, I no longer see crashes when I
keep making and breaking the SSH tunnel while running "vmstat 1" in an
SSH session over a socket that is running through that tunnel.

Simon-
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