RE: [patch] tcp: attach SYNACK messages to request sockets instead of listener

[Haiyang Zhang <haiyangz@microsoft.com>]

> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@gmail.com]
> Sent: Friday, October 30, 2015 4:19 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: edumazet@google.com; David Miller <davem@davemloft.net>;
> netdev@vger.kernel.org; KY Srinivasan <kys@microsoft.com>
> Subject: Re: [patch] tcp: attach SYNACK messages to request sockets
> instead of listener
> 
> On Fri, 2015-10-30 at 13:02 -0700, Eric Dumazet wrote:
> 
> > So it looks like you have a device with a very big hh_len
> >
> > MAX_TCP_HEADER is not enough space to hold all headers, and this is
> the
> > bug that needs to be fixed. This is scary to realloc all tcp packets !
> >
> 
> drivers/net/hyperv/netvsc_drv.c sets a needed_headroom of 220 bytes :(
> 
> Could you try :
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 4ac653b7b8ac..7dbdd29076be 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -132,8 +132,10 @@ static inline bool dev_xmit_complete(int rc)
>   *	used.
>   */
> 
> -#if defined(CONFIG_WLAN) || IS_ENABLED(CONFIG_AX25)
> -# if defined(CONFIG_MAC80211_MESH)
> +#if defined(CONFIG_WLAN) || IS_ENABLED(CONFIG_AX25) ||
> IS_ENABLED(CONFIG_HYPERV_NET)
> +# if IS_ENABLED(CONFIG_HYPERV_NET)
> +# define LL_MAX_HEADER 384
> +# elif defined(CONFIG_MAC80211_MESH)
>  #  define LL_MAX_HEADER 128
>  # else
>  #  define LL_MAX_HEADER 96
> 

With your 2nd patch, I saw:
[   19.242104] Wow ! headroom=164 while hh_len(eth0)=240

After adding the 3rd patch with increased LL_MAX_HEADER,
the warning and stack trace no longer show up.

Also, could you fix the net core code so that it doesn't 
panic even with reallocated header?

Thanks,
- Haiyang