[PATCH v4 4/4] selftests: net: add a virtio_net deadlock selftest

Bui Quang Minh
2025-04-17T07:29:44Z

The selftest reproduces the deadlock scenario when binding/unbinding XDP
program, XDP socket, rx ring resize on virtio_net interface.

Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
---
.../testing/selftests/drivers/net/hw/Makefile | 1 +
.../selftests/drivers/net/hw/virtio_net.py | 65 +++++++++++++++++++
2 files changed, 66 insertions(+)
create mode 100755 tools/testing/selftests/drivers/net/hw/virtio_net.py

diff --git a/tools/testing/selftests/drivers/net/hw/Makefile b/tools/testing/selftests/drivers/net/hw/Makefile
index 07cddb19ba35..b5af7c1412bf 100644
--- a/tools/testing/selftests/drivers/net/hw/Makefile
+++ b/tools/testing/selftests/drivers/net/hw/Makefile
@@ -21,6 +21,7 @@ TEST_PROGS = \
rss_ctx.py \
rss_input_xfrm.py \
tso.py \
+ virtio_net.py \
#

TEST_FILES := \
diff --git a/tools/testing/selftests/drivers/net/hw/virtio_net.py b/tools/testing/selftests/drivers/net/hw/virtio_net.py
new file mode 100755
index 000000000000..7cad7ab98635
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/hw/virtio_net.py
@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+# This is intended to be run on a virtio-net guest interface.
+# The test binds the XDP socket to the interface without setting
+# the fill ring to trigger delayed refill_work. This helps to
+# make it easier to reproduce the deadlock when XDP program,
+# XDP socket bind/unbind, rx ring resize race with refill_work on
+# the buggy kernel.
+#
+# The Qemu command to setup virtio-net
+# -netdev tap,id=hostnet1,vhost=on,script=no,downscript=no
+# -device virtio-net-pci,netdev=hostnet1,iommu_platform=on,disable-legacy=on
+
+from lib.py import ksft_exit, ksft_run
+from lib.py import KsftSkipEx, KsftFailEx
+from lib.py import NetDrvEnv
+from lib.py import bkg, ip, cmd, ethtool
+import re
+
+def _get_rx_ring_entries(cfg):
+ output = ethtool(f"-g {cfg.ifname}").stdout
+ values = re.findall(r'RX:\s+(\d+)', output)
+ return int(values[1])
+
+def setup_xsk(cfg, xdp_queue_id = 0) -> bkg:
+ # Probe for support
+ xdp = cmd(f'{cfg.net_lib_dir / "xdp_helper"} - -', fail=False)
+ if xdp.ret == 255:
+ raise KsftSkipEx('AF_XDP unsupported')
+ elif xdp.ret > 0:
+ raise KsftFailEx('unable to create AF_XDP socket')
+
+ try:
+ xsk_bkg = bkg(f'{cfg.net_lib_dir / "xdp_helper"} {cfg.ifindex} ' \
+ '{xdp_queue_id} -z', ksft_wait=3)
+ return xsk_bkg
+ except:
+ raise KsftSkipEx('Failed to bind XDP socket in zerocopy. ' \
+ 'Please consider adding iommu_platform=on ' \
+ 'when setting up virtio-net-pci')
+
+def check_xdp_bind(cfg):
+ ip(f"link set dev %s xdp obj %s sec xdp" %
+ (cfg.ifname, cfg.net_lib_dir / "xdp_dummy.bpf.o"))
+ ip(f"link set dev %s xdp off" % cfg.ifname)
+
+def check_rx_resize(cfg, queue_size = 128):
+ rx_ring = _get_rx_ring_entries(cfg)
+ ethtool(f"-G %s rx %d" % (cfg.ifname, queue_size))
+ ethtool(f"-G %s rx %d" % (cfg.ifname, rx_ring))
+
+def main():
+ with NetDrvEnv(__file__, nsim_test=False) as cfg:
+ try:
+ xsk_bkg = setup_xsk(cfg)
+ except KsftSkipEx as e:
+ print(f"WARN: xsk pool is not set up, err: {e}")
+
+ ksft_run([check_xdp_bind, check_rx_resize],
+ args=(cfg, ))
+ ksft_exit()
+
+if __name__ == "__main__":
+ main()
--
2.43.0