Merge branch 'net_sched-sch_sfq-reject-limit-of-1'

Octavian Purdila says:

====================
net_sched: sch_sfq: reject limit of 1

The implementation does not properly support limits of 1. Add an
in-kernel check, in addition to existing iproute2 check, since other
tools may be used for configuration.

This patch set also adds a selfcheck to test that a limit of 1 is
rejected.

An alternative (or in addition) we could fix the implementation by
setting q->tail to NULL in sfq_drop if this is the last slot we marked
empty, e.g.:

  --- a/net/sched/sch_sfq.c
  +++ b/net/sched/sch_sfq.c
  @@ -317,8 +317,11 @@ static unsigned int sfq_drop(struct Qdisc *sch, struct sk_buff **to_free)
                  /* It is difficult to believe, but ALL THE SLOTS HAVE LENGTH 1. */
                  x = q->tail->next;
                  slot = &q->slots[x];
  -               q->tail->next = slot->next;
                  q->ht[slot->hash] = SFQ_EMPTY_SLOT;
  +               if (x == slot->next)
  +                       q->tail = NULL; /* no more active slots */
  +               else
  +                       q->tail->next = slot->next;
                  goto drop;
          }
====================

Link: https://patch.msgid.link/20241204030520.2084663-1-tavip@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/sch_sfq.c

@@ -652,6 +652,10 @@ static int sfq_change(struct Qdisc *sch, struct nlattr *opt,
 		if (!p)
 			return -ENOMEM;
 	}
+	if (ctl->limit == 1) {
+		NL_SET_ERR_MSG_MOD(extack, "invalid limit");
+		return -EINVAL;
+	}
 	sch_tree_lock(sch);
 	if (ctl->quantum)
 		q->quantum = ctl->quantum;

tools/testing/selftests/tc-testing/scripts/sfq_rejects_limit_1.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+#
+# Script that checks that SFQ rejects a limit of 1 at the kernel
+# level. We can't use iproute2's tc because it does not accept a limit
+# of 1.
+
+import sys
+import os
+
+from pyroute2 import IPRoute
+from pyroute2.netlink.exceptions import NetlinkError
+
+ip = IPRoute()
+ifidx = ip.link_lookup(ifname=sys.argv[1])
+
+try:
+    ip.tc('add', 'sfq', ifidx, limit=1)
+    sys.exit(1)
+except NetlinkError:
+    sys.exit(0)

tools/testing/selftests/tc-testing/tc-tests/qdiscs/sfq.json

@@ -208,5 +208,25 @@
         "teardown": [
             "$TC qdisc del dev $DUMMY handle 1: root"
         ]
+    },
+    {
+        "id": "4d6f",
+        "name": "Check that limit of 1 is rejected",
+        "category": [
+            "qdisc",
+            "sfq"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "./scripts/sfq_rejects_limit_1.py $DUMMY",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "sfq",
+        "matchCount": "0",
+        "teardown": [
+        ]
     }
 ]