netdev - Re: [PATCH bpf v4 13/14] bpf/tests: Fix error in tail call limit tests

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Date:   Tue, 14 Sep 2021 20:55:00 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Johan Almbladh <johan.almbladh@...finetworks.com>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Cc:     kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, iii@...ux.ibm.com,
        paul@...ium.io, netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf v4 13/14] bpf/tests: Fix error in tail call limit
 tests

On 09/14/2021 08:41 PM, Tiezhu Yang wrote:
> On 09/14/2021 05:18 PM, Johan Almbladh wrote:
>> This patch fixes an error in the tail call limit test that caused the
>> test to fail on for x86-64 JIT. Previously, the register R0 was used to
>> report the total number of tail calls made. However, after a tail call
>> fall-through, the value of the R0 register is undefined. Now, all tail
>> call error path tests instead use context state to store the count.
>>
>> Fixes: 874be05f525e ("bpf, tests: Add tail call test suite")
>> Reported-by: Paul Chaignon <paul@...ium.io>
>> Reported-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>> Signed-off-by: Johan Almbladh <johan.almbladh@...finetworks.com>
>> ---
>>   lib/test_bpf.c | 37 +++++++++++++++++++++++++++----------
>>   1 file changed, 27 insertions(+), 10 deletions(-)
>>
>> diff --git a/lib/test_bpf.c b/lib/test_bpf.c
>> index 7475abfd2186..ddb9a8089d2e 100644
>> --- a/lib/test_bpf.c
>> +++ b/lib/test_bpf.c
>> @@ -12179,10 +12179,15 @@ static __init int test_bpf(void)
>>   struct tail_call_test {
>>       const char *descr;
>>       struct bpf_insn insns[MAX_INSNS];
>> +    int flags;
>>       int result;
>>       int stack_depth;
>>   };
>>   +/* Flags that can be passed to tail call test cases */
>> +#define FLAG_NEED_STATE        BIT(0)
>> +#define FLAG_RESULT_IN_STATE    BIT(1)
>> +
>>   /*
>>    * Magic marker used in test snippets for tail calls below.
>>    * BPF_LD/MOV to R2 and R2 with this immediate value is replaced
>> @@ -12252,32 +12257,38 @@ static struct tail_call_test 
>> tail_call_tests[] = {
>>       {
>>           "Tail call error path, max count reached",
>>           .insns = {
>> -            BPF_ALU64_IMM(BPF_ADD, R1, 1),
>> -            BPF_ALU64_REG(BPF_MOV, R0, R1),
>> +            BPF_LDX_MEM(BPF_W, R2, R1, 0),
>> +            BPF_ALU64_IMM(BPF_ADD, R2, 1),
>> +            BPF_STX_MEM(BPF_W, R1, R2, 0),
>>               TAIL_CALL(0),
>>               BPF_EXIT_INSN(),
>>           },
>> -        .result = MAX_TAIL_CALL_CNT + 1,
>> +        .flags = FLAG_NEED_STATE | FLAG_RESULT_IN_STATE,
>> +        .result = (MAX_TAIL_CALL_CNT + 1 + 1) * MAX_TESTRUNS,
>
> Hi Johan,
>
> I have tested this patch,
> It should be "MAX_TAIL_CALL_CNT + 1" instead of "MAX_TAIL_CALL_CNT + 1 
> + 1"?

Oh, sorry, it is right when MAX_TAIL_CALL_CNT is 32,
I have tested it based on MAX_TAIL_CALL_CNT is 33,
so I need to modify here if MAX_TAIL_CALL_CNT is 33 in my v3 patch.

Tested-by: Tiezhu Yang <yangtiezhu@...ngson.cn>

>
> [...]
>
> Thanks,
> Tiezhu