selftests: drv-net: test drivers sleeping in ndo_get_stats64

Most of our tests use rtnetlink to read device stats, so they
don't expose the drivers much to paths in which device stats
are read under RCU. Add tests which hammer profcs reads to
make sure drivers:
 - don't sleep while reporting stats,
 - can handle parallel reads,
 - can handle device going down while reading.

Set ifname on the env class in NetDrvEnv, we already do that
in NetDrvEpEnv.

  KTAP version 1
  1..7
  ok 1 stats.check_pause
  ok 2 stats.check_fec
  ok 3 stats.pkt_byte_sum
  ok 4 stats.qstat_by_ifindex
  ok 5 stats.check_down
  ok 6 stats.procfs_hammer
  # completed up/down cycles: 6
  ok 7 stats.procfs_downup_hammer
  # Totals: pass:7 fail:0 xfail:0 xpass:0 skip:0 error:0

Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250107022932.2087744-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/lib/py/env.py

@@ -48,6 +48,7 @@ class NetDrvEnv:
         else:
             self._ns = NetdevSimDev(**kwargs)
             self.dev = self._ns.nsims[0].dev
+        self.ifname = self.dev['ifname']
         self.ifindex = self.dev['ifindex']
 
     def __enter__(self):

tools/testing/selftests/drivers/net/stats.py

@@ -2,12 +2,15 @@
 # SPDX-License-Identifier: GPL-2.0
 
 import errno
+import subprocess
+import time
 from lib.py import ksft_run, ksft_exit, ksft_pr
-from lib.py import ksft_ge, ksft_eq, ksft_in, ksft_true, ksft_raises, KsftSkipEx, KsftXfailEx
+from lib.py import ksft_ge, ksft_eq, ksft_is, ksft_in, ksft_lt, ksft_true, ksft_raises
+from lib.py import KsftSkipEx, KsftXfailEx
 from lib.py import ksft_disruptive
 from lib.py import EthtoolFamily, NetdevFamily, RtnlFamily, NlError
 from lib.py import NetDrvEnv
-from lib.py import ip, defer
+from lib.py import cmd, ip, defer
 
 ethnl = EthtoolFamily()
 netfam = NetdevFamily()
@@ -174,10 +177,95 @@ def check_down(cfg) -> None:
     netfam.qstats_get({"ifindex": cfg.ifindex, "scope": "queue"}, dump=True)
 
 
+def __run_inf_loop(body):
+    body = body.strip()
+    if body[-1] != ';':
+        body += ';'
+
+    return subprocess.Popen(f"while true; do {body} done", shell=True,
+                            stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+
+
+def __stats_increase_sanely(old, new) -> None:
+    for k in old.keys():
+        ksft_ge(new[k], old[k])
+        ksft_lt(new[k] - old[k], 1 << 31, comment="likely wrapping error")
+
+
+def procfs_hammer(cfg) -> None:
+    """
+    Reading stats via procfs only holds the RCU lock, which is not an exclusive
+    lock, make sure drivers can handle parallel reads of stats.
+    """
+    one = __run_inf_loop("cat /proc/net/dev")
+    defer(one.kill)
+    two = __run_inf_loop("cat /proc/net/dev")
+    defer(two.kill)
+
+    time.sleep(1)
+    # Make sure the processes are running
+    ksft_is(one.poll(), None)
+    ksft_is(two.poll(), None)
+
+    rtstat1 = rtnl.getlink({"ifi-index": cfg.ifindex})['stats64']
+    time.sleep(2)
+    rtstat2 = rtnl.getlink({"ifi-index": cfg.ifindex})['stats64']
+    __stats_increase_sanely(rtstat1, rtstat2)
+    # defers will kill the loops
+
+
+@ksft_disruptive
+def procfs_downup_hammer(cfg) -> None:
+    """
+    Reading stats via procfs only holds the RCU lock, drivers often try
+    to sleep when reading the stats, or don't protect against races.
+    """
+    # Max out the queues, we'll flip between max and 1
+    channels = ethnl.channels_get({'header': {'dev-index': cfg.ifindex}})
+    if channels['combined-count'] == 0:
+        rx_type = 'rx'
+    else:
+        rx_type = 'combined'
+    cur_queue_cnt = channels[f'{rx_type}-count']
+    max_queue_cnt = channels[f'{rx_type}-max']
+
+    cmd(f"ethtool -L {cfg.ifname} {rx_type} {max_queue_cnt}")
+    defer(cmd, f"ethtool -L {cfg.ifname} {rx_type} {cur_queue_cnt}")
+
+    # Real test stats
+    stats = __run_inf_loop("cat /proc/net/dev")
+    defer(stats.kill)
+
+    ipset = f"ip link set dev {cfg.ifname}"
+    defer(ip, f"link set dev {cfg.ifname} up")
+    # The "echo -n 1" lets us count iterations below
+    updown = f"{ipset} down; sleep 0.05; {ipset} up; sleep 0.05; " + \
+             f"ethtool -L {cfg.ifname} {rx_type} 1; " + \
+             f"ethtool -L {cfg.ifname} {rx_type} {max_queue_cnt}; " + \
+              "echo -n 1"
+    updown = __run_inf_loop(updown)
+    kill_updown = defer(updown.kill)
+
+    time.sleep(1)
+    # Make sure the processes are running
+    ksft_is(stats.poll(), None)
+    ksft_is(updown.poll(), None)
+
+    rtstat1 = rtnl.getlink({"ifi-index": cfg.ifindex})['stats64']
+    # We're looking for crashes, give it extra time
+    time.sleep(9)
+    rtstat2 = rtnl.getlink({"ifi-index": cfg.ifindex})['stats64']
+    __stats_increase_sanely(rtstat1, rtstat2)
+
+    kill_updown.exec()
+    stdout, _ = updown.communicate(timeout=5)
+    ksft_pr("completed up/down cycles:", len(stdout.decode('utf-8')))
+
+
 def main() -> None:
     with NetDrvEnv(__file__, queue_count=100) as cfg:
         ksft_run([check_pause, check_fec, pkt_byte_sum, qstat_by_ifindex,
-                  check_down],
+                  check_down, procfs_hammer, procfs_downup_hammer],
                  args=(cfg, ))
     ksft_exit()