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: sta...@vger.kernel.org # 4.11.x > Signed-off-by: Timur Tabi <ti...@codeaurora.org> > --- > 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
