From mboxrd@z Thu Jan 1 00:00:00 1970 From: Florian Fainelli Subject: Re: [PATCH 1/2] [for 4.13] net: qcom/emac: disable flow control autonegotiation by default Date: Tue, 1 Aug 2017 14:55:19 -0700 Message-ID: <1af0df70-c8a9-f327-abba-9c977c4dfdc9@gmail.com> References: <1501623460-3575-1-git-send-email-timur@codeaurora.org> <1501623460-3575-2-git-send-email-timur@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit To: Timur Tabi , "David S. Miller" , netdev@vger.kernel.org Return-path: Received: from mail-wm0-f66.google.com ([74.125.82.66]:36894 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752465AbdHAVzX (ORCPT ); Tue, 1 Aug 2017 17:55:23 -0400 Received: by mail-wm0-f66.google.com with SMTP id t138so4887693wmt.4 for ; Tue, 01 Aug 2017 14:55:23 -0700 (PDT) In-Reply-To: <1501623460-3575-2-git-send-email-timur@codeaurora.org> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 08/01/2017 02:37 PM, Timur Tabi wrote: > The EMAC has a curious qwirk when RX flow control is enabled and the > kernel hangs. With the kernel hung, the EMAC's RX queue soon fills. > If RX flow control is enabled, the EMAC will then send a non-stop > stream of pause frames until the system is reset. The EMAC does not > have a built-in watchdog. > > In various tests, the pause frame stream sometimes overloads nearby > switches, effectively disabling the network. Since the RX queue is > large and the host processor is more than capable of handling incoming > packets quickly, the only time the EMAC will send any pause frames is > when the kernel is hung and unrecoverable. This is not specific to your EMAC, a lot of adapters have this problem actually. I wonder if it would make sense to reach for a broader solution where we could have a networking stack panic/oops notifier which will actively clean up the active network devices' RX queue(s) and if tx_pause was enabled, disable it. We could have drivers announce themselves as needing this either via NETIF_F_* feature bit or some other private flag. > > To avoid all these problems, we disable flow control autonegotiation > by default, and only enable receiving pause frames. > > Cc: stable@vger.kernel.org # 4.11.x > Signed-off-by: Timur Tabi > --- > drivers/net/ethernet/qualcomm/emac/emac.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/ethernet/qualcomm/emac/emac.c b/drivers/net/ethernet/qualcomm/emac/emac.c > index 60850bfa3d32..475c0ea29235 100644 > --- a/drivers/net/ethernet/qualcomm/emac/emac.c > +++ b/drivers/net/ethernet/qualcomm/emac/emac.c > @@ -441,8 +441,13 @@ static void emac_init_adapter(struct emac_adapter *adpt) > /* others */ > adpt->preamble = EMAC_PREAMBLE_DEF; > > - /* default to automatic flow control */ > - adpt->automatic = true; > + /* Disable transmission of pause frames by default, to avoid the > + * risk of a pause frame flood that can occur if the kernel hangs. > + * We still want to be able to respond to them, however. > + */ > + adpt->automatic = false; > + adpt->tx_flow_control = false; > + adpt->rx_flow_control = true; > } > > /* Get the clock */ > -- Florian