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The key observation is that drivers using netif_tx_start_all_queues() are prone to experiencing a stall when reconfiguration completes compared to drivers using netif_tx_wake_all_queues(). start_all_queues only clears DRV_XOFF, while wake_all_queues also calls __netif_schedule() to kick the qdisc. Without the kick, qdisc backlog present at reconfig time can stay stuck until a new trigger is issued. The test caps the TX ring at 64 entries so it fills quickly, then installs FQ on a target TX queue and sends UDP packets with SO_TXTIME scheduled in the future. With napi_defer_hard_irqs slowing completions, the small ring can fill when FQ releases the burst, leaving requeued qdisc backlog with no FQ timer to rescue it. A subsequent ring reconfig must wake the queues to drain the backlog. Simply starting the queues can leave it stuck. On host with problematic driver: Sent 128 SO_TXTIME packets (+100ms) Sent 128 SO_TXTIME packets (+200ms) Backlog before reconfig: 52632 bytes Check| At /root/ksft-net-drv/./drivers/net/ring_reconfig.py, ... Check| ksft_eq(0, backlog, Check failed 0 != 52632 qdisc backlog stuck on queue 1 after ring reconfig not ok 3 ring_reconfig.reconfig_tx_stall On host with fixed driver: Sent 128 SO_TXTIME packets (+100ms) Sent 128 SO_TXTIME packets (+200ms) Backlog before reconfig: 76024 bytes ok 3 ring_reconfig.reconfig_tx_stall Signed-off-by: Mohsin Bashir Signed-off-by: Jakub Kicinski --- Changelog: V2: - Reoreder config file changes to handle check_selftest failure - Chain exception with from exc in _create_sotxtime_socket - Use getattr to get arch-specific value for SO_TXTIME, fallback to 61 V1: https://lore.kernel.org/netdev/20260612001754.2489868-1-mohsin.bashr@gmail.com --- tools/testing/selftests/drivers/net/config | 4 + .../selftests/drivers/net/ring_reconfig.py | 176 +++++++++++++++++- 2 files changed, 178 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/drivers/net/config b/tools/testing/selftests/drivers/net/config index 617de8aaf551..1ef07fae74c1 100644 --- a/tools/testing/selftests/drivers/net/config +++ b/tools/testing/selftests/drivers/net/config @@ -4,6 +4,10 @@ CONFIG_DEBUG_INFO_BTF_MODULES=n CONFIG_INET_PSP=y CONFIG_IPV6=y CONFIG_MACSEC=m +CONFIG_NET_ACT_SKBEDIT=m +CONFIG_NET_CLS_ACT=y +CONFIG_NET_CLS_FLOWER=m +CONFIG_NET_CLS_MATCHALL=m CONFIG_NETCONSOLE=m CONFIG_NETCONSOLE_DYNAMIC=y CONFIG_NETCONSOLE_EXTENDED_LOG=y diff --git a/tools/testing/selftests/drivers/net/ring_reconfig.py b/tools/testing/selftests/drivers/net/ring_reconfig.py index f9530a8b0856..11491a0b7013 100755 --- a/tools/testing/selftests/drivers/net/ring_reconfig.py +++ b/tools/testing/selftests/drivers/net/ring_reconfig.py @@ -5,10 +5,18 @@ Test channel and ring size configuration via ethtool (-L / -G). """ +import socket +import struct +import time + from lib.py import ksft_run, ksft_exit, ksft_pr from lib.py import ksft_eq +from lib.py import KsftSkipEx from lib.py import NetDrvEpEnv, EthtoolFamily, GenerateTraffic -from lib.py import defer, NlError +from lib.py import cmd, defer, rand_port, tc, NlError + +# Added in Python 3.13; fallback to 61 for x86/ARM/MIPS +SO_TXTIME = getattr(socket, "SO_TXTIME", 61) def channels(cfg) -> None: @@ -151,6 +159,169 @@ def ringparam(cfg) -> None: GenerateTraffic(cfg).wait_pkts_and_stop(10000) +def _write_sysfs(cfg, path, val): + with open(path, "r", encoding="utf-8") as fp: + orig_val = fp.read().strip() + if str(val) == orig_val: + return + with open(path, "w", encoding="utf-8") as fp: + fp.write(str(val)) + defer(lambda p=path, v=orig_val: open(p, "w").write(v)) + + +def _get_mq_handle(cfg): + qdiscs = tc(f"qdisc show dev {cfg.ifname}", json=True) + for q in qdiscs: + if q.get("kind") == "mq": + return q["handle"] + raise KsftSkipEx(f"no mq qdisc found on {cfg.ifname}") + + +def _get_qdisc_backlog(cfg, queue, mq_handle): + qdiscs = tc(f"-s qdisc show dev {cfg.ifname}", json=True) + target_parent = f"{mq_handle}{queue + 1:x}" + for q in qdiscs: + if q.get("parent", "") == target_parent: + return q.get("backlog") + return None + + +def _setup_fq_qdisc(cfg, mq_handle, port, target_queue, other_queue): + mq_child_parent = f"{mq_handle}{target_queue + 1:x}" + + # Save the original child qdisc to restore after test + qdiscs = tc(f"qdisc show dev {cfg.ifname}", json=True) + default_qdisc = cmd("sysctl -n net.core.default_qdisc").stdout.strip() + orig_kind = default_qdisc + for q in qdiscs: + if q.get("parent", "") == mq_child_parent: + orig_kind = q.get("kind", default_qdisc) + break + try: + tc(f"qdisc replace dev {cfg.ifname} parent {mq_child_parent} fq") + except Exception as exc: + raise KsftSkipEx("fq not available (CONFIG_NET_SCH_FQ)") from exc + defer(tc, + f"qdisc replace dev {cfg.ifname} parent {mq_child_parent} {orig_kind}") + + qdisc_j = tc(f"qdisc show dev {cfg.ifname}", json=True) + has_clsact = any(q['kind'] == 'clsact' for q in qdisc_j) + if not has_clsact: + tc(f"qdisc add dev {cfg.ifname} clsact") + defer(tc, f"qdisc del dev {cfg.ifname} clsact") + + proto = "ipv6" if int(cfg.addr_ipver) == 6 else "ip" + try: + tc(f"filter add dev {cfg.ifname} egress protocol {proto} " + f"pref 1 flower ip_proto udp dst_port {port} " + f"action skbedit queue_mapping {target_queue}") + except Exception as exc: + raise KsftSkipEx("tc flower/act_skbedit not available") from exc + defer(tc, f"filter del dev {cfg.ifname} egress pref 1") + + tc(f"filter add dev {cfg.ifname} egress pref 100 " + f"matchall action skbedit queue_mapping {other_queue}") + defer(tc, f"filter del dev {cfg.ifname} egress pref 100") + + +def _create_sotxtime_socket(cfg): + sock = socket.socket(socket.AF_INET6 if cfg.addr_ipver == "6" + else socket.AF_INET, socket.SOCK_DGRAM) + try: + sock.setsockopt(socket.SOL_SOCKET, SO_TXTIME, struct.pack("Ii", 1, 0)) + except OSError as exc: + sock.close() + raise KsftSkipEx("SO_TXTIME not supported") from exc + sock.setsockopt(socket.SOL_SOCKET, socket.SO_BINDTODEVICE, + cfg.ifname.encode()) + return sock + + +def _send_sotxtime_burst(sock, addr, port, count, delay_ns, ipver): + payload = b'\x00' * 1400 + txtime_ns = time.clock_gettime_ns(time.CLOCK_MONOTONIC) + delay_ns + + ancdata = [(socket.SOL_SOCKET, SO_TXTIME, struct.pack("Q", txtime_ns))] + if int(ipver) == 6: + dest = (addr, port, 0, 0) + else: + dest = (addr, port) + for _ in range(count): + sock.sendmsg([payload], ancdata, 0, dest) + + +def reconfig_tx_stall(cfg) -> None: + target_queue = 1 + other_queue = 0 + + ehdr = {'header': {'dev-index': cfg.ifindex}} + chans = cfg.eth.channels_get(ehdr) + + if 'combined-max' not in chans: + raise KsftSkipEx("device does not support combined channels") + if chans['combined-count'] < 2: + raise KsftSkipEx("need at least 2 combined channels") + + rings = cfg.eth.rings_get(ehdr) + if 'rx' not in rings or 'tx' not in rings: + raise KsftSkipEx("device does not expose rx/tx ring params") + tx_cur = rings['tx'] + if tx_cur <= 64: + raise KsftSkipEx("tx ring size already at minimum") + defer(cfg.eth.rings_set, ehdr | {'tx': tx_cur}) + + tx_min = 64 + cfg.eth.rings_set(ehdr | {'tx': tx_min}) + + # Slow completions so the ring stays full after FQ releases packets + napi_defer = f"/sys/class/net/{cfg.ifname}/napi_defer_hard_irqs" + gro_timeout = f"/sys/class/net/{cfg.ifname}/gro_flush_timeout" + _write_sysfs(cfg, napi_defer, 100) + _write_sysfs(cfg, gro_timeout, 1000000000) + + mq_handle = _get_mq_handle(cfg) + port = rand_port() + _setup_fq_qdisc(cfg, mq_handle, port, target_queue, other_queue) + + sock = _create_sotxtime_socket(cfg) + defer(sock.close) + + pkt_count = tx_min * 2 + + for delay_ms in [100, 200, 500]: + delay_ns = delay_ms * 1_000_000 + _send_sotxtime_burst(sock, cfg.remote_addr, port, pkt_count, + delay_ns, cfg.addr_ipver) + ksft_pr(f"Sent {pkt_count} SO_TXTIME packets (+{delay_ms}ms)") + time.sleep(delay_ms / 1000 + 0.3) + + backlog = _get_qdisc_backlog(cfg, target_queue, mq_handle) + if backlog: + break + else: + raise KsftSkipEx("failed to build qdisc backlog") + + ksft_pr(f"Backlog before reconfig: {backlog} bytes") + + # Trigger ring reconfig — driver should call wake, not just start + cfg.eth.rings_set(ehdr | {'tx': tx_cur}) + + # Let completions proceed normally + _write_sysfs(cfg, napi_defer, 0) + _write_sysfs(cfg, gro_timeout, 0) + + # Poll for backlog to drain + for _ in range(100): + backlog = _get_qdisc_backlog(cfg, target_queue, mq_handle) + if not backlog: + break + time.sleep(0.1) + + ksft_eq(0, backlog, + comment=f"qdisc backlog stuck on queue {target_queue} " + f"after ring reconfig") + + def main() -> None: """ Ksft boiler plate main """ @@ -158,7 +329,8 @@ def main() -> None: cfg.eth = EthtoolFamily() ksft_run([channels, - ringparam], + ringparam, + reconfig_tx_stall], args=(cfg, )) ksft_exit() -- 2.52.0