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Merge branch 'replace-direct-dequeue-call-with-qdisc_dequeue_peeked'

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Jamal Hadi Salim says:

====================
Replace direct dequeue call with qdisc_dequeue_peeked

When sfb and red qdiscs have children (eg qfq qdisc) whose peek() callback is
qdisc_peek_dequeued(), we could get a kernel panic. When the parent of such
qdiscs (eg illustrated in patch #3 as tbf) wants to retrieve an skb from
its child (red/sfb in this case), it will do the following:
 1a. do a peek() - and when sensing there's an skb the child can offer, then
     - the child in this case(red/sfb) calls its child's (qfq) peek.
        qfq does the right thing and will return the gso_skb queue packet.
        Note: if there wasnt a gso_skb entry then qfq will store it there.
 1b. invoke a dequeue() on the child (red/sfb). And herein lies the problem.
     - red/sfb will call the child's dequeue() which will essentially just
       try to grab something of qfq's queue.

The right thing to do in #1b is to grab the skb off gso_skb queue.
This patchset fixes that issue by changing #1b to use qdisc_dequeue_peeked()
method instead.

Patch 1 fixes the issue for red qdisc. Patch 2 fixes it for sfb.
Patch 3 adds testcases for the two setups.
====================

Link: https://patch.msgid.link/20260430152957.194015-1-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jakub Kicinski
2026-05-02 10:21:00 -07:00
parent 383d0fb894 3a3a30c14d
commit 386829cd89
3 changed files with 150 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/sched/sch_red.c
+1 -1
View File
@@ -162,7 +162,7 @@ static struct sk_buff *red_dequeue(struct Qdisc *sch)
struct red_sched_data *q = qdisc_priv(sch);
struct Qdisc *child = q->qdisc;
skb = child->dequeue(child);
skb = qdisc_dequeue_peeked(child);
if (skb) {
qdisc_bstats_update(sch, skb);
qdisc_qstats_backlog_dec(sch, skb);
net/sched/sch_sfb.c
+1 -1
View File
@@ -441,7 +441,7 @@ static struct sk_buff *sfb_dequeue(struct Qdisc *sch)
struct Qdisc *child = q->qdisc;
struct sk_buff *skb;
skb = child->dequeue(q->qdisc);
skb = qdisc_dequeue_peeked(child);
if (skb) {
qdisc_bstats_update(sch, skb);
tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json
+148
View File
@@ -1136,5 +1136,153 @@
"teardown": [
"$TC qdisc del dev $DUMMY handle 1: root"
]
},
{
"id": "7a5f",
"name": "Force red to dequeue from its child's gso_skb with qfq leaf",
"category": [
"qdisc",
"tbf",
"red",
"qfq"
],
"plugins": {
"requires": "nsPlugin"
},
"setup": [
"$IP link set dev $DUMMY up || true",
"$IP addr add 10.10.11.10/24 dev $DUMMY || true",
"$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b",
"$TC qdisc add dev $DUMMY parent 1: handle 2: red limit 757 min 16 max 24 avpkt 16",
"$TC qdisc add dev $DUMMY parent 2: handle 3: qfq",
"$TC class add dev $DUMMY classid 3:1 parent 3: qfq maxpkt 512 weight 1",
"$TC filter add dev $DUMMY parent 3: protocol ip prio 1 matchall classid 3:1 action ok"
],
"cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true",
"expExitCode": "0",
"verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:",
"matchJSON": [
{
"kind": "red",
"handle": "2:",
"bytes": 98,
"packets": 1,
"backlog": 0,
"qlen": 0
}
],
"teardown": [
"$TC qdisc del dev $DUMMY handle 1: root"
]
},
{
"id": "cdae",
"name": "Force sfb to dequeue from its child's gso_skb with qfq leaf",
"category": [
"qdisc",
"tbf",
"sfb",
"qfq"
],
"plugins": {
"requires": "nsPlugin"
},
"setup": [
"$IP link set dev $DUMMY up || true",
"$IP addr add 10.10.11.10/24 dev $DUMMY || true",
"$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b",
"$TC qdisc add dev $DUMMY parent 1: handle 2: sfb",
"$TC qdisc add dev $DUMMY parent 2: handle 3: qfq",
"$TC class add dev $DUMMY classid 3:1 parent 3: qfq maxpkt 512 weight 1",
"$TC filter add dev $DUMMY parent 3: protocol ip prio 1 matchall classid 3:1 action ok"
],
"cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true",
"expExitCode": "0",
"verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:",
"matchJSON": [
{
"kind": "sfb",
"handle": "2:",
"bytes": 98,
"packets": 1,
"backlog": 0,
"qlen": 0
}
],
"teardown": [
"$TC qdisc del dev $DUMMY handle 1: root"
]
},
{
"id": "291d",
"name": "Force red to dequeue from its child's gso_skb with dualpi2 leaf",
"category": [
"qdisc",
"tbf",
"red",
"dualpi2"
],
"plugins": {
"requires": "nsPlugin"
},
"setup": [
"$IP link set dev $DUMMY up || true",
"$IP addr add 10.10.11.10/24 dev $DUMMY || true",
"$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b",
"$TC qdisc add dev $DUMMY parent 1: handle 2: red limit 757 min 16 max 24 avpkt 16",
"$TC qdisc add dev $DUMMY parent 2: handle 3: dualpi2"
],
"cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true",
"expExitCode": "0",
"verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:",
"matchJSON": [
{
"kind": "red",
"handle": "2:",
"bytes": 98,
"packets": 1,
"backlog": 0,
"qlen": 0
}
],
"teardown": [
"$TC qdisc del dev $DUMMY handle 1: root"
]
},
{
"id": "9c6d",
"name": "Force sfb to dequeue from its child's gso_skb with dualpi2 leaf",
"category": [
"qdisc",
"tbf",
"sfb",
"dualpi2"
],
"plugins": {
"requires": "nsPlugin"
},
"setup": [
"$IP link set dev $DUMMY up || true",
"$IP addr add 10.10.11.10/24 dev $DUMMY || true",
"$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b",
"$TC qdisc add dev $DUMMY parent 1: handle 2: sfb",
"$TC qdisc add dev $DUMMY parent 2: handle 3: dualpi2"
],
"cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true",
"expExitCode": "0",
"verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:",
"matchJSON": [
{
"kind": "sfb",
"handle": "2:",
"bytes": 98,
"packets": 1,
"backlog": 0,
"qlen": 0
}
],
"teardown": [
"$TC qdisc del dev $DUMMY handle 1: root"
]
}
]