[lucid] cherry-pick BUG->WARN change in tun

[Stefan Bader]

On 01/13/2011 04:38 PM, dann frazier wrote:
> Please consider pulling the following change into lucid. This resolves
> LP #698883.
> 
> SRU Justification:
>  Avoids crash
> Impact:
>  BUG() causes system to crash
> Fix:
>  Upstream reduced BUG() to a WARN_ON_ONCE w/ additional diagnostic info.
>  Upstream commit ef3db4a5954281bc1ea49a4739c88eaea091dc71.
> Testcase:
>  A tractable case would presumably require packet injection. Otherwise, a long
>  stable run on a configuration that has hit this problem before.
> 
> This was originally reported by a customer in restricted LP #680356. A
> custom kernel w/ this fix was applied and neither the issue nor a
> regression has been observed in the following month.
> 
> Upstream change follows - it cherry-picks cleanly into the lucid git tree.
> 
> commit ef3db4a5954281bc1ea49a4739c88eaea091dc71
> Author: Michael S. Tsirkin <mst at redhat.com>
> Date: Wed Jul 21 04:32:45 2010 +0000
> 
>     tun: avoid BUG, dump packet on GSO errors
> 
>     There are still some LRO cards that cause GSO errors in tun,
>     and BUG on this is an unfriendly way to tell the admin
>     to disable LRO.
> 
>     Further, experience shows we might have more GSO bugs lurking.
>     See https://bugzilla.kernel.org/show_bug.cgi?id=16413
>     as a recent example.
>     dumping a packet will make it easier to figure it out.
> 
>     Replace BUG with warning+dump+drop the packet to make
>     GSO errors in tun less critical and easier to debug.
> 
>     Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
>     Tested-by: Alex Unigovsky <unik at compot.ru>
>     Acked-by: Herbert Xu <herbert at gondor.apana.org.au>
>     Signed-off-by: David S. Miller <davem at davemloft.net>
> 

Sounds reasonable to me. May be also a candidate for hinting towards upstream
longterm before .35

Acked-by: Stefan Bader <stefan.bader at canonical.com>