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Date:   Sat, 27 Jul 2019 19:16:16 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Stanislav Fomichev <sdf@...ichev.me>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 0/9] Revamp test_progs as a test running framework

On Sat, Jul 27, 2019 at 6:12 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sat, Jul 27, 2019 at 12:02 PM Andrii Nakryiko <andriin@...com> wrote:
> >
> > This patch set makes a number of changes to test_progs selftest, which is
> > a collection of many other tests (and sometimes sub-tests as well), to provide
> > better testing experience and allow to start convering many individual test
> > programs under selftests/bpf into a single and convenient test runner.
>
> I really like the patches, but something isn't right:

Argh... Uninitialized `int ret` in test__vprintf(). Should be
initialized to zero, otherwise in some corner cases when log buffer is
completely full and ret's initial value is sufficiently large negative
number, it can underflow env.log_cnt, silently skipping one log
output, and then crashing on next one. You've somehow encountered a
fascinating series of conditions that I've never stumbled upon running
my code dozens of times. Fixing, sorry about that!

> #16 raw_tp_writable_reject_nbd_invalid:OK
> #17 raw_tp_writable_test_run:OK
> #18 reference_tracking:OK
> [   87.715996] test_progs[2200]: segfault at 2f ip 00007f56aeea347b sp
> 00007ffce9720980 error 4 in libc-2.23.so[7f56aee5b000+198000]
> [   87.717316] Code: ff ff 44 89 8d 30 fb ff ff e8 01 74 fd ff 44 8b
> 8d 30 fb ff ff 4c 8b 85 28 fb ff ff e9 fd eb ff ff 31 c0 48 83 c9 ff
> 4c 89 df <f2> ae c7 85 28 fb ff ff 00 00 00 00 48 89 c8 48 f7 d0 4c 8f
> [   87.719493] audit: type=1701 audit(1564276195.971:5): auid=0 uid=0
> gid=0 ses=1 subj=kernel pid=2200 comm="test_progs"
> exe="/data/users/ast/net-next/tools/testing/selftests/bpf/test_progs"
> sig=11 res=1
> Segmentation fault (core dumped)
>
> Under gdb fault is different:
> #23 stacktrace_build_id:OK
> Detaching after fork from child process 2276.
> Detaching after fork from child process 2278.
> [  149.013116] perf: interrupt took too long (6799 > 6713), lowering
> kernel.perf_event_max_sample_rate to 29000
> [  149.014634] perf: interrupt took too long (8511 > 8498), lowering
> kernel.perf_event_max_sample_rate to 23000
> [  149.017038] perf: interrupt took too long (10649 > 10638), lowering
> kernel.perf_event_max_sample_rate to 18000
> [  149.021901] perf: interrupt took too long (13322 > 13311), lowering
> kernel.perf_event_max_sample_rate to 15000
> [  149.042946] perf: interrupt took too long (16660 > 16652), lowering
> kernel.perf_event_max_sample_rate to 12000
> Detaching after fork from child process 2279.
> #24 stacktrace_build_id_nmi:OK
> #25 stacktrace_map:OK
> #26 stacktrace_map_raw_tp:OK
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x00007ffff723f47b in vfprintf () from /usr/lib/libc.so.6
> (gdb) bt
> #0  0x00007ffff723f47b in vfprintf () from /usr/lib/libc.so.6
> #1  0x00007ffff72655a9 in vsnprintf () from /usr/lib/libc.so.6
> #2  0x0000000000403100 in test__vprintf (fmt=0x426754 "%s:PASS:%s %d
> nsec\n", args=0x7fffffffe878) at test_progs.c:114
> #3  0x000000000040325c in test__printf (fmt=fmt@...ry=0x426754
> "%s:PASS:%s %d nsec\n") at test_progs.c:147
> #4  0x000000000042222d in test_task_fd_query_rawtp () at
> prog_tests/task_fd_query_rawtp.c:19
> #5  0x0000000000402c76 in main (argc=<optimized out>, argv=<optimized
> out>) at test_progs.c:501
> (gdb) info threads
>   Id   Target Id         Frame
> * 1    Thread 0x7ffff7fea700 (LWP 2245) "test_progs"
> 0x00007ffff723f47b in vfprintf () from /usr/lib/libc.so.6

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