Date: Thu, 8 Jun 2023 13:08:00 -0300
From: Pedro Tammela <pctammela@...atatu.com>
To: renmingshuai <renmingshuai@...wei.com>
Cc: caowangbao@...wei.com, davem@...emloft.net, edumazet@...gle.com,
 jhs@...atatu.com, jiri@...nulli.us, kuba@...nel.org, liaichun@...wei.com,
 linux-kernel@...r.kernel.org, liubo335@...wei.com, netdev@...r.kernel.org,
 pabeni@...hat.com, xiyou.wangcong@...il.com, yanan@...wei.com
Subject: Re: [PATCH v2] net/sched: Set the flushing flags to false to prevent
 an infinite loop and add one test to tdc

On 08/06/2023 09:32, renmingshuai wrote:
>> 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@...alhost ~]# tc qdisc add dev eth2 root handle 1: htb default 1
> [root@...alhost ~]# tc chain add dev eth2
> [root@...alhost ~]# tc filter del dev eth2 chain 0 parent 1: prio 0
> [root@...alhost ~]# 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@...alhost 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@...wei.com>

Please respin with the following applied:

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 c759c3db9a37..361235ad574b 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
@@ -125,25 +125,5 @@
          "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 $DEV1 root handle 1: htb default 1"
-        ]
      }
  ]
diff --git 
a/tools/testing/selftests/tc-testing/tc-tests/infra/filters.json 
b/tools/testing/selftests/tc-testing/tc-tests/infra/filters.
json
new file mode 100644
index 000000000000..55d6f209c388
--- /dev/null
+++ b/tools/testing/selftests/tc-testing/tc-tests/infra/filters.json
@@ -0,0 +1,24 @@
+[
+    {
+        "id": "c2b4",
+        "name": "Adding a new filter after flushing empty chain doesnt 
cause an infinite loop",
+        "category": [
+            "filter",
+            "chain"
+        ],
+        "setup": [
+            "$IP link add dev $DUMMY type dummy || /bin/true",
+            "$TC qdisc add dev $DUMMY root handle 1: htb default 1",
+            "$TC chain add dev $DUMMY",
+            "$TC filter del dev $DUMMY chain 0 parent 1: prio 0"
+        ],
+        "cmdUnderTest": "$TC filter add dev $DUMMY chain 0 parent 1:",
+        "expExitCode": "2",
+        "verifyCmd": "$TC chain ls dev $DUMMY",
+        "matchPattern": "chain parent 1: chain 0",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY root handle 1: htb default 1"
+        ]
+    }
+]

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