Re: [PATCH bpf-next v8 10/10] selftests/bpf: test case for register_bpf_struct_ops().

[Kui-Feng Lee <sinquersw@gmail.com>]

On 11/1/23 18:43, Martin KaFai Lau wrote:
> On 10/31/23 5:30 PM, Kui-Feng Lee wrote:
>>
>>
>> On 10/30/23 23:59, Martin KaFai Lau wrote:
>>> On 10/30/23 12:28 PM, thinker.li@gmail.com wrote:
>>>> diff --git 
>>>> a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c 
>>>> b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
>>>> new file mode 100644
>>>> index 000000000000..3a00dc294583
>>>> --- /dev/null
>>>> +++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
>>>> @@ -0,0 +1,39 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
>>>> +#include <test_progs.h>
>>>> +#include <time.h>
>>>> +
>>>> +#include "rcu_tasks_trace_gp.skel.h"
>>>> +#include "struct_ops_module.skel.h"
>>>> +
>>>> +static void test_regular_load(void)
>>>> +{
>>>> +    struct struct_ops_module *skel;
>>>> +    struct bpf_link *link;
>>>> +    DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
>>>> +    int err;
>>>> +
>>>> +    skel = struct_ops_module__open_opts(&opts);
>>>> +    if (!ASSERT_OK_PTR(skel, "struct_ops_module_open"))
>>>> +        return;
>>>> +    err = struct_ops_module__load(skel);
>>>> +    if (!ASSERT_OK(err, "struct_ops_module_load"))
>>>> +        return;
>>>> +
>>>> +    link = bpf_map__attach_struct_ops(skel->maps.testmod_1);
>>>> +    ASSERT_OK_PTR(link, "attach_test_mod_1");
>>>> +
>>>> +    /* test_2() will be called from bpf_dummy_reg() in 
>>>> bpf_testmod.c */
>>>> +    ASSERT_EQ(skel->bss->test_2_result, 7, "test_2_result");
>>>> +
>>>> +    bpf_link__destroy(link);
>>>> +
>>>> +    struct_ops_module__destroy(skel);
>>>> +}
>>>> +
>>>> +void serial_test_struct_ops_module(void)
>>>> +{
>>>> +    if (test__start_subtest("regular_load"))
>>>> +        test_regular_load();
>>>
>>> Could it also add some negative tests, e.g. missing 'struct 
>>> bpf_struct_ops_common_value', reg() when the module is gone...etc.
>>>
>>> [ ... ]
>>>
>>>> +/* This function will trigger call_rcu_tasks_trace() in the kernel */
>>>> +static int kern_sync_rcu_tasks_trace(void)
>>>
>>> With patch 4, is it still needed?
>>
>> Patch 4 shortens time of holding the module, but it still can happen
>> since bpf_link_put() is performed asynchronously.
> 
> Is the link pinned to a file that triggers bpf_link_put()?
> Otherwise, close() should reach bpf_link_put_direct() which is synchronous.
> 
> Even if it went through bpf_link_put(), rcu_tasks_trace_gp is very 
> specific to the bpf sleepable tracing prog. Is it the correct one to wait?

You are right! We don't test pinned link. I will remove this part.

> 
>>
>>>
>>>> +{
>>>> +    struct rcu_tasks_trace_gp *rcu;
>>>> +    time_t start;
>>>> +    long gp_seq;
>>>> +    LIBBPF_OPTS(bpf_test_run_opts, opts);
>>>> +
>>>> +    rcu = rcu_tasks_trace_gp__open_and_load();
>>>> +    if (IS_ERR(rcu))
>>>> +        return -EFAULT;
>>>> +    if (rcu_tasks_trace_gp__attach(rcu))
>>>> +        return -EFAULT;
>>>> +
>>>> +    gp_seq = READ_ONCE(rcu->bss->gp_seq);
>>>> +
>>>> +    if 
>>>> (bpf_prog_test_run_opts(bpf_program__fd(rcu->progs.do_call_rcu_tasks_trace),
>>>> +                   &opts))
>>>> +        return -EFAULT;
>>>> +    if (opts.retval != 0)
>>>> +        return -EFAULT;
>>>> +
>>>> +    start = time(NULL);
>>>> +    while ((start + 2) > time(NULL) &&
>>>> +           gp_seq == READ_ONCE(rcu->bss->gp_seq))
>>>> +        sched_yield();
>>>> +
>>>> +    rcu_tasks_trace_gp__destroy(rcu);
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>>   /*
>>>>    * Trigger synchronize_rcu() in kernel.
>>>>    */
>>>>   int kern_sync_rcu(void)
>>>>   {
>>>> +    if (kern_sync_rcu_tasks_trace())
>>>> +        return -EFAULT;
>>>>       return syscall(__NR_membarrier, MEMBARRIER_CMD_SHARED, 0, 0);
>>>>   }
>>>
>