selftests: drv-net-hw: add test for memory allocation failures with page pool

Bugs in memory allocation failure paths are quite common.
Add a test exercising those paths based on qstat and page pool
failure hook.

Running on bnxt:

  # ./drivers/net/hw/pp_alloc_fail.py
  KTAP version 1
  1..1
  # ethtool -G change retval: success
  ok 1 pp_alloc_fail.test_pp_alloc
  # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0

I initially wrote this test to validate commit be43b7489a ("net/mlx5e:
RX, Fix page_pool allocation failure recovery for striding rq") but mlx5
still doesn't have qstat. So I run it on bnxt, and while bnxt survives
I found the problem fixed in commit 7301177307 ("eth: bnxt: fix counting
packets discarded due to OOM and netpoll").

Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20240429144426.743476-7-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/hw/Makefile

@@ -9,6 +9,7 @@ TEST_PROGS = \
 	hw_stats_l3.sh \
 	hw_stats_l3_gre.sh \
 	loopback.sh \
+	pp_alloc_fail.py \
 	#
 
 TEST_FILES := \

tools/testing/selftests/drivers/net/hw/pp_alloc_fail.py

@@ -0,0 +1,129 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import time
+import os
+from lib.py import ksft_run, ksft_exit, ksft_pr
+from lib.py import KsftSkipEx, KsftFailEx
+from lib.py import NetdevFamily, NlError
+from lib.py import NetDrvEpEnv
+from lib.py import cmd, tool, GenerateTraffic
+
+
+def _write_fail_config(config):
+    for key, value in config.items():
+        with open("/sys/kernel/debug/fail_function/" + key, "w") as fp:
+            fp.write(str(value) + "\n")
+
+
+def _enable_pp_allocation_fail():
+    if not os.path.exists("/sys/kernel/debug/fail_function"):
+        raise KsftSkipEx("Kernel built without function error injection (or DebugFS)")
+
+    if not os.path.exists("/sys/kernel/debug/fail_function/page_pool_alloc_pages"):
+        with open("/sys/kernel/debug/fail_function/inject", "w") as fp:
+            fp.write("page_pool_alloc_pages\n")
+
+    _write_fail_config({
+        "verbose": 0,
+        "interval": 511,
+        "probability": 100,
+        "times": -1,
+    })
+
+
+def _disable_pp_allocation_fail():
+    if not os.path.exists("/sys/kernel/debug/fail_function"):
+        return
+
+    if os.path.exists("/sys/kernel/debug/fail_function/page_pool_alloc_pages"):
+        with open("/sys/kernel/debug/fail_function/inject", "w") as fp:
+            fp.write("\n")
+
+    _write_fail_config({
+        "probability": 0,
+        "times": 0,
+    })
+
+
+def test_pp_alloc(cfg, netdevnl):
+    def get_stats():
+        return netdevnl.qstats_get({"ifindex": cfg.ifindex}, dump=True)[0]
+
+    def check_traffic_flowing():
+        stat1 = get_stats()
+        time.sleep(1)
+        stat2 = get_stats()
+        if stat2['rx-packets'] - stat1['rx-packets'] < 15000:
+            raise KsftFailEx("Traffic seems low:", stat2['rx-packets'] - stat1['rx-packets'])
+
+
+    try:
+        stats = get_stats()
+    except NlError as e:
+        if e.nl_msg.error == -95:
+            stats = {}
+        else:
+            raise
+    if 'rx-alloc-fail' not in stats:
+        raise KsftSkipEx("Driver does not report 'rx-alloc-fail' via qstats")
+
+    set_g = False
+    traffic = None
+    try:
+        traffic = GenerateTraffic(cfg)
+
+        check_traffic_flowing()
+
+        _enable_pp_allocation_fail()
+
+        s1 = get_stats()
+        time.sleep(3)
+        s2 = get_stats()
+
+        if s2['rx-alloc-fail'] - s1['rx-alloc-fail'] < 1:
+            raise KsftSkipEx("Allocation failures not increasing")
+        if s2['rx-alloc-fail'] - s1['rx-alloc-fail'] < 100:
+            raise KsftSkipEx("Allocation increasing too slowly", s2['rx-alloc-fail'] - s1['rx-alloc-fail'],
+                             "packets:", s2['rx-packets'] - s1['rx-packets'])
+
+        # Basic failures are fine, try to wobble some settings to catch extra failures
+        check_traffic_flowing()
+        g = tool("ethtool", "-g " + cfg.ifname, json=True)[0]
+        if 'rx' in g and g["rx"] * 2 <= g["rx-max"]:
+            new_g = g['rx'] * 2
+        elif 'rx' in g:
+            new_g = g['rx'] // 2
+        else:
+            new_g = None
+
+        if new_g:
+            set_g = cmd(f"ethtool -G {cfg.ifname} rx {new_g}", fail=False).ret == 0
+            if set_g:
+                ksft_pr("ethtool -G change retval: success")
+            else:
+                ksft_pr("ethtool -G change retval: did not succeed", new_g)
+        else:
+                ksft_pr("ethtool -G change retval: did not try")
+
+        time.sleep(0.1)
+        check_traffic_flowing()
+    finally:
+        _disable_pp_allocation_fail()
+        if traffic:
+            traffic.stop()
+        time.sleep(0.1)
+        if set_g:
+            cmd(f"ethtool -G {cfg.ifname} rx {g['rx']}")
+
+
+def main() -> None:
+    netdevnl = NetdevFamily()
+    with NetDrvEpEnv(__file__, nsim_test=False) as cfg:
+
+        ksft_run([test_pp_alloc], args=(cfg, netdevnl, ))
+    ksft_exit()
+
+
+if __name__ == "__main__":
+    main()

tools/testing/selftests/net/lib/py/ksft.py

@@ -11,6 +11,10 @@ KSFT_RESULT = None
 KSFT_RESULT_ALL = True
 
 
+class KsftFailEx(Exception):
+    pass
+
+
 class KsftSkipEx(Exception):
     pass