netdev - Re: [PATCH bpf-next 2/2] selftests/bpf: add loop test 5

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Date:   Sun, 4 Aug 2019 05:45:23 +0000
From:   Yonghong Song <yhs@...com>
To:     Alexei Starovoitov <ast@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "Kernel Team" <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: add loop test 5



On 8/2/19 4:33 PM, Alexei Starovoitov wrote:
> Add a test with multiple exit conditions.
> It's not an infinite loop only when the verifier can properly track
> all math on variable 'i' through all possible ways of executing this loop.

Agreed with motivation of this test.

> 
> barrier()s are needed to disable llvm optimization that combines multiple
> branches into fewer branches.
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>   .../bpf/prog_tests/bpf_verif_scale.c          |  1 +
>   tools/testing/selftests/bpf/progs/loop5.c     | 37 +++++++++++++++++++
>   2 files changed, 38 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/progs/loop5.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
> index 757e39540eda..29615a4a9362 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
> @@ -72,6 +72,7 @@ void test_bpf_verif_scale(void)
>   		{ "loop1.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
>   		{ "loop2.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
>   		{ "loop4.o", BPF_PROG_TYPE_RAW_TRACEPOINT }, > +		{ "loop5.o", BPF_PROG_TYPE_RAW_TRACEPOINT },

More like a BPF_PROG_TYPE_SCHED_CLS type although probably it does not 
matter as we did not attach it to anywhere?

>   
>   		/* partial unroll. 19k insn in a loop.
>   		 * Total program size 20.8k insn.
> diff --git a/tools/testing/selftests/bpf/progs/loop5.c b/tools/testing/selftests/bpf/progs/loop5.c
> new file mode 100644
> index 000000000000..9d9817efe208
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/loop5.c
> @@ -0,0 +1,37 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2019 Facebook
> +#include <linux/sched.h>
> +#include <linux/ptrace.h>

The above headers probably not needed.

> +#include <stdint.h>
> +#include <stddef.h>
> +#include <stdbool.h>
> +#include <linux/bpf.h>
> +#include "bpf_helpers.h"
> +#define barrier() __asm__ __volatile__("": : :"memory")
> +
> +char _license[] SEC("license") = "GPL";
> +
> +SEC("socket")
> +int while_true(volatile struct __sk_buff* skb)
> +{
> +	int i = 0;
> +
> +	while (true) {
> +		if (skb->len)
> +			i += 3;
> +		else
> +			i += 7;
> +		if (i == 9)
> +			break;
> +		barrier();
> +		if (i == 10)
> +			break;
> +		barrier();
> +		if (i == 13)
> +			break;
> +		barrier();
> +		if (i == 14)
> +			break;
> +	}
> +	return i;
> +}
>