Date: Tue, 20 Nov 2012 10:21:34 -0500 From: Karim Fodil-Lemelin <fodillemlinkarim@gmail.com> To: Gleb Smirnoff <glebius@FreeBSD.org> Cc: Karim Fodil-Lemelin <fodillemlinkarim@gmail.com>, jfv@FreeBSD.org, freebsd-net@FreeBSD.org Subject: Re: igb diver crashes in head@241037 Message-ID: <50AB9FFE.70401@gmail.com> In-Reply-To: <20121120111833.GC67660@FreeBSD.org> References: <50AA8F24.7080604@gmail.com> <20121120111833.GC67660@FreeBSD.org>
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Gleb, On 20/11/2012 6:18 AM, Gleb Smirnoff wrote: > Karim, > > On Mon, Nov 19, 2012 at 02:57:24PM -0500, Karim Fodil-Lemelin wrote: > K> While testing the latest igb driver in CURRENT I came across an issue > K> with igb_mq_start(). More specifically this code: > K> > K> ... > K> > K> struct mbuf *pm = NULL; > K> /* > K> ** Try to queue first to avoid > K> ** out-of-order delivery, but > K> ** settle for it if that fails > K> */ > K> if (m && drbr_enqueue(ifp, txr->br, m)) > K> pm = m; > K> err = igb_mq_start_locked(ifp, txr, pm); > K> > K> ... > K> > K> > K> The problem comes from the fact that drbr_enqueue() can return an error > K> and delete the mbuf as seen in drbr_enqueue(): > K> > K> ... > K> error = buf_ring_enqueue(br, m); > K> if (error) > K> m_freem(m); > K> ... > > Good catch! > > K> diff --git a/sys/dev/e1000/if_igb.c b/sys/dev/e1000/if_igb.c > K> index 1318910..be1719a 100644 > K> --- a/sys/dev/e1000/if_igb.c > K> +++ b/sys/dev/e1000/if_igb.c > K> @@ -961,15 +961,7 @@ igb_mq_start(struct ifnet *ifp, struct mbuf *m) > K> que = &adapter->queues[i]; > K> if (((txr->queue_status & IGB_QUEUE_DEPLETED) == 0) && > K> IGB_TX_TRYLOCK(txr)) { > K> - struct mbuf *pm = NULL; > K> - /* > K> - ** Try to queue first to avoid > K> - ** out-of-order delivery, but > K> - ** settle for it if that fails > K> - */ > K> - if (m && drbr_enqueue(ifp, txr->br, m)) > K> - pm = m; > K> - err = igb_mq_start_locked(ifp, txr, pm); > K> + err = igb_mq_start_locked(ifp, txr, m); > K> IGB_TX_UNLOCK(txr); > K> } else { > K> err = drbr_enqueue(ifp, txr->br, m); > > Well, the idea to prevent out-of-order delivery is important. TCP > suffers a lot when this happens. > > I'd suggest the following code: > > if (m) > drbr_enqueue(ifp, txr->br, m); > err = igb_mq_start_locked(ifp, txr, NULL); > > Which eventually leads us to all invocations of igb_mq_start_locked() called > with third argument as NULL. This allows us to simplify this function. > > Patch for review attached. > > In my case I use ALTQ and in igb_mq_start_locked() it calls drbr_needs_enqueue() which always return 1 with ALTQ. So I did not see the out of order issue. I do think your patch makes sense though and I'm also thinking that em_mq_start() could also benefit from the same logic. Regards, Karim.
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