[PATCH v2] net/sched: Set the flushing flags to false to prevent an infinite loop and add one test to tdc
From: renmingshuai
Date: Thu Jun 08 2023 - 08:33:04 EST
>On 07/06/2023 01:19, renmingshuai wrote:
>>> On 06/06/2023 11:45, renmingshuai wrote:
>>>> When a new chain is added by using tc, one soft lockup alarm will
>>>> be
>>>> generated after delete the prio 0 filter of the chain. To
>>>> reproduce
>>>> the problem, perform the following steps:
>>>> (1) tc qdisc add dev eth0 root handle 1: htb default 1
>>>> (2) tc chain add dev eth0
>>>> (3) tc filter del dev eth0 chain 0 parent 1: prio 0
>>>> (4) tc filter add dev eth0 chain 0 parent 1:
>>>
>>> This seems like it could be added to tdc or 3 and 4 must be run in
>>> parallel?
>> 3 and 4 do not need to be run inparallel. When a new chain is added
>> by the
>> way as step 1 and the step 3 is completed, this problem always
>> occurs
>> whenever step 4 is run.
>
>Got it,
>The test still hangs with the provided patch.
>
>+ tc qdisc add dev lo root handle 1: htb default 1
>+ tc chain add dev lo
>+ tc filter del dev lo chain 0 parent 1: prio 0
>[ 68.790030][ T6704] [+]
>[ 68.790060][ T6704] chain refcnt 2
>[ 68.790951][ T6704] [-]
>+ tc filter add dev lo chain 0 parent 1:
><hangs>
>
>Also please add this test to tdc, it should be straightforward.
>
Sorry for not testing before. I forgot that the chain->refcnt was
increased by 1 when tcf_chain_get() is called in tc_del_tfilter().
The value of chain->refcnt is 2 after chain flush. The test
result is as follows:
[root@localhost ~]# tc qdisc add dev eth2 root handle 1: htb default 1
[root@localhost ~]# tc chain add dev eth2
[root@localhost ~]# tc filter del dev eth2 chain 0 parent 1: prio 0
[root@localhost ~]# tc filter add dev eth2 chain 0 parent 1:
Error: Filter kind and protocol must be specified.
We have an error talking to the kernel
And I have add this test to tdc:
[root@localhost tc-testing]# ./tdc.py -f tc-tests/filters/tests.json
ok 7 c2b4 - Adding a new fiter after deleting a filter in a chain does
not cause an infinite loop
Fixes: 726d061286ce ("net: sched: prevent insertion of new classifiers during chain flush")
Signed-off-by: renmingshuai <renmingshuai@xxxxxxxxxx>
---
net/sched/cls_api.c | 7 +++++
.../tc-testing/tc-tests/filters/tests.json | 26 ++++++++++++++++---
2 files changed, 30 insertions(+), 3 deletions(-)
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 2621550bfddc..3ea054e03fbf 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -2442,6 +2442,13 @@ static int tc_del_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
tfilter_notify_chain(net, skb, block, q, parent, n,
chain, RTM_DELTFILTER, extack);
tcf_chain_flush(chain, rtnl_held);
+ /* Set the flushing flags to false to prevent an infinite loop
+ * when a new filter is added.
+ */
+ mutex_lock(&chain->filter_chain_lock);
+ if (chain->refcnt == 2)
+ chain->flushing = false;
+ mutex_unlock(&chain->filter_chain_lock);
err = 0;
goto errout;
}
diff --git a/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json b/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
index 361235ad574b..f165ca091109 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
@@ -125,5 +125,25 @@
"teardown": [
"$TC qdisc del dev $DEV2 ingress"
]
+ },
+ {
+ "id": "c2b4",
+ "name": "Adding a new fiter after deleting a filter in a chain does not cause an infinite loop",
+ "category": [
+ "filter",
+ "prio"
+ ],
+ "setup": [
+ "$TC qdisc add dev $DEV1 root handle 1: htb default 1",
+ "$TC chain add dev $DEV1"
+ ],
+ "cmdUnderTest": "$TC filter del dev $DEV1 chain 0 parent 1: prio 0",
+ "expExitCode": "0",
+ "verifyCmd": "$TC filter add dev $DEV1 chain 0 parent 1:",
+ "matchPattern": "Error: Filter kind and protocol must be specified.",
+ "matchCount": "1",
+ "teardown": [
+ "$TC qdisc del dev $DEV1 root handle 1: htb default 1"
+ ]
}
]
--
2.27.0
>>>>
>>>>
>>>> The refcnt of the chain added by step 2 is equal to 1. After step
>>>> 3,
>>>> the flushing flag of the chain is set to true in the
>>>> tcf_chain_flush()
>>>> called by tc_del_tfilter() because the prio is 0. In this case,
>>>> if
>>>> we add a new filter to this chain, it will never succeed and try
>>>> again
>>>> and again because the refresh flash is always true and refcnt is
>>>> 1.
>>>> A soft lock alarm is generated 20 seconds later.
>>>> The stack is show as below:
>>>>
>>>> Kernel panic - not syncing: softlockup: hung tasks
>>>> CPU: 2 PID: 3321861 Comm: tc Kdump: loaded Tainted: G
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
>>>> Call Trace:
>>>> <IRQ>
>>>> dump_stack+0x57/0x6e
>>>> panic+0x196/0x3ec
>>>> watchdog_timer_fn.cold+0x16/0x5c
>>>> __run_hrtimer+0x5e/0x190
>>>> __hrtimer_run_queues+0x8a/0xe0
>>>> hrtimer_interrupt+0x110/0x2c0
>>>> ? irqtime_account_irq+0x49/0xf0
>>>> __sysvec_apic_timer_interrupt+0x5f/0xe0
>>>> asm_call_irq_on_stack+0x12/0x20
>>>> </IRQ>
>>>> sysvec_apic_timer_interrupt+0x72/0x80
>>>> asm_sysvec_apic_timer_interrupt+0x12/0x20
>>>> RIP: 0010:mutex_lock+0x24/0x70
>>>> RSP: 0018:ffffa836004ab9a8 EFLAGS: 00000246
>>>> RAX: 0000000000000000 RBX: ffff95bb02d76700 RCX: 0000000000000000
>>>> RDX: ffff95bb27462100 RSI: 0000000000000000 RDI: ffff95ba5b527000
>>>> RBP: ffff95ba5b527000 R08: 0000000000000001 R09: ffffa836004abbb8
>>>> R10: 000000000000000f R11: 0000000000000000 R12: 0000000000000000
>>>> R13: ffff95ba5b527000 R14: ffffa836004abbb8 R15: 0000000000000001
>>>> __tcf_chain_put+0x27/0x200
>>>> tc_new_tfilter+0x5e8/0x810
>>>> ? tc_setup_cb_add+0x210/0x210
>>>> rtnetlink_rcv_msg+0x2e3/0x380
>>>> ? rtnl_calcit.isra.0+0x120/0x120
>>>> netlink_rcv_skb+0x50/0x100
>>>> netlink_unicast+0x12d/0x1d0
>>>> netlink_sendmsg+0x286/0x490
>>>> sock_sendmsg+0x62/0x70
>>>> ____sys_sendmsg+0x24c/0x2c0
>>>> ? import_iovec+0x17/0x20
>>>> ? sendmsg_copy_msghdr+0x80/0xa0
>>>> ___sys_sendmsg+0x75/0xc0
>>>> ? do_fault_around+0x118/0x160
>>>> ? do_read_fault+0x68/0xf0
>>>> ? __handle_mm_fault+0x3f9/0x6f0
>>>> __sys_sendmsg+0x59/0xa0
>>>> do_syscall_64+0x33/0x40
>>>> entry_SYSCALL_64_after_hwframe+0x61/0xc6
>>>> RIP: 0033:0x7f96705b8247
>>>> RSP: 002b:00007ffe552e9dc8 EFLAGS: 00000246 ORIG_RAX:
>>>> 000000000000002e
>>>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f96705b8247
>>>> RDX: 0000000000000000 RSI: 00007ffe552e9e40 RDI: 0000000000000003
>>>> RBP: 0000000000000001 R08: 0000000000000001 R09: 0000558113f678b0
>>>> R10: 00007f967069ab00 R11: 0000000000000246 R12: 00000000647ea089
>>>> R13: 00007ffe552e9f30 R14: 0000000000000001 R15: 0000558113175f00
>>>>
>>>> To avoid this case, set chain->flushing to be false if the
>>>> chain->refcnt
>>>> is 1 after flushing the chain when prio is 0.
>>>>
>>>> Fixes: 726d061286ce ("net: sched: prevent insertion of new
>>>> classifiers during chain flush")
>>>> Signed-off-by: Ren Mingshuai <renmingshuai@xxxxxxxxxx>
>>>> ---
>>>> net/sched/cls_api.c | 7 +++++++
>>>> 1 file changed, 7 insertions(+)
>>>>
>>>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>>>> index 2621550bfddc..68be55d75831 100644
>>>> --- a/net/sched/cls_api.c
>>>> +++ b/net/sched/cls_api.c
>>>> @@ -2442,6 +2442,13 @@ static int tc_del_tfilter(struct sk_buff
>>>> *skb, struct nlmsghdr *n,
>>>> tfilter_notify_chain(net, skb, block, q, parent,
>>>> n,
>>>> chain, RTM_DELTFILTER,
>>>> extack);
>>>> tcf_chain_flush(chain, rtnl_held);
>>>> + /* Set the flushing flags to false to prevent an
>>>> infinite loop
>>>> + * when a new filter is added.
>>>> + */
>>>> + mutex_lock(&chain->filter_chain_lock);
>>>> + if (chain->refcnt == 1)
>>>> + chain->flushing = false;
>>>> + mutex_unlock(&chain->filter_chain_lock);
>>>> err = 0;
>>>> goto errout;
>>>> }