From 12b5717990c81fc2f6f2aa9d53d960b916478d4f Mon Sep 17 00:00:00 2001 From: Magnus Karlsson Date: Wed, 25 Jan 2023 08:48:58 +0100 Subject: [PATCH] lan966x: execute xdp_do_flush() before napi_complete_done() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Make sure that xdp_do_flush() is always executed before napi_complete_done(). This is important for two reasons. First, a redirect to an XSKMAP assumes that a call to xdp_do_redirect() from napi context X on CPU Y will be followed by a xdp_do_flush() from the same napi context and CPU. This is not guaranteed if the napi_complete_done() is executed before xdp_do_flush(), as it tells the napi logic that it is fine to schedule napi context X on another CPU. Details from a production system triggering this bug using the veth driver can be found following the first link below. The second reason is that the XDP_REDIRECT logic in itself relies on being inside a single NAPI instance through to the xdp_do_flush() call for RCU protection of all in-kernel data structures. Details can be found in the second link below. Fixes: a825b611c7c1 ("net: lan966x: Add support for XDP_REDIRECT") Signed-off-by: Magnus Karlsson Acked-by: Toke Høiland-Jørgensen Acked-by: Steen Hegelund Link: https://lore.kernel.org/r/20221220185903.1105011-1-sbohrer@cloudflare.com Link: https://lore.kernel.org/all/20210624160609.292325-1-toke@redhat.com/ Signed-off-by: Jakub Kicinski --- drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c index 5314c064ceae73..55b484b1056275 100644 --- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c @@ -608,12 +608,12 @@ static int lan966x_fdma_napi_poll(struct napi_struct *napi, int weight) lan966x_fdma_rx_reload(rx); } - if (counter < weight && napi_complete_done(napi, counter)) - lan_wr(0xff, lan966x, FDMA_INTR_DB_ENA); - if (redirect) xdp_do_flush(); + if (counter < weight && napi_complete_done(napi, counter)) + lan_wr(0xff, lan966x, FDMA_INTR_DB_ENA); + return counter; }