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

[Martin KaFai Lau <martin.lau@linux.dev>]

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?

> 
>>
>>> +{
>>> +    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);
>>>   }
>>