Bringing a linked netdevsim device down and then up causes communication failure because both interfaces lack carrier. Basically a ifdown/ifup on the interface make the link broken. Commit 3762ec05a9fbda ("netdevsim: add NAPI support") added supported for NAPI, calling netif_carrier_off() in nsim_stop(). This patch re-enables the carrier symmetrically on nsim_open(), in case the device is linked and the peer is up. Signed-off-by: Breno Leitao Fixes: 3762ec05a9fbda ("netdevsim: add NAPI support") Reviewed-by: Andrew Lunn --- Changes in v2: - Reword the commit message to reference the symmetry between nsim_open() and nsim_stop() in regarding to carrier. (Andrew Lunn) - Link to v1: https://lore.kernel.org/r/20251013-netdevsim_fix-v1-1-357b265dd9d0@debian.org --- drivers/net/netdevsim/netdev.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c index ebc3833e95b44..fa1d97885caaf 100644 --- a/drivers/net/netdevsim/netdev.c +++ b/drivers/net/netdevsim/netdev.c @@ -545,6 +545,7 @@ static void nsim_enable_napi(struct netdevsim *ns) static int nsim_open(struct net_device *dev) { struct netdevsim *ns = netdev_priv(dev); + struct netdevsim *peer; int err; netdev_assert_locked(dev); @@ -555,6 +556,12 @@ static int nsim_open(struct net_device *dev) nsim_enable_napi(ns); + peer = rtnl_dereference(ns->peer); + if (peer && netif_running(peer->netdev)) { + netif_carrier_on(dev); + netif_carrier_on(peer->netdev); + } + return 0; } --- base-commit: 0b4b77eff5f8cd9be062783a1c1e198d46d0a753 change-id: 20251013-netdevsim_fix-b9a8a5064f8f Best regards, -- Breno Leitao