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Date:      Thu, 6 Jul 2017 22:47:05 -0300
From:      Luiz Otavio O Souza <lists.br@gmail.com>
To:        Marius Strobl <marius@freebsd.org>
Cc:        Vincenzo Maffione <v.maffione@gmail.com>, FreeBSD Net <freebsd-net@freebsd.org>
Subject:   Re: NULL pointer dereference bug triggered by netmap
Message-ID:  <CAB=2f8z0e9bzVaH2Xo0%2BUa0ENW5jbkeh1a_RtZ2Qb%2BMHo6f-Jg@mail.gmail.com>
In-Reply-To: <20170705110512.GA28058@alchemy.franken.de>
References:  <CA%2B_eA9goJ6j=q6UO-%2BfOt-aHVgFmujQfH8WfYEHf9=PQobdwHg@mail.gmail.com> <20170705110512.GA28058@alchemy.franken.de>

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On 5 July 2017 at 08:05, Marius Strobl wrote:
> On Mon, Jul 03, 2017 at 05:08:09PM +0200, Vincenzo Maffione wrote:
>> Details here:
>>
>> https://github.com/luigirizzo/netmap/issues/322
>>
>> Is it acceptable to commit the proposed patch?
>
> As suggested by hselasky@, the outliner problem at hand is better solved
> by a dummy if_start method in order to not hurt the fast-path. Thus, if
> anything at all, a KASSERT(ifp->if_start != NULL, "no if_start method")
> should be added to if_handoff() and if_start().

As noted by ae@, if_transmit() is not supported on the loopback
interface.  In any case, the loopback interface could provide a dummy
if_transmit() method to not queue the packets, not call if_start() and
print a warning/panic.

Luiz



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