netdev - selftests/bpf test

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Date:   Tue, 24 Jul 2018 08:45:44 -0700
From:   Yonghong Song <yhs@...com>
To:     John Fastabend <john.fastabend@...il.com>,
        netdev <netdev@...r.kernel.org>
CC:     Yonghong Song <yhs@...com>, Martin Lau <kafai@...com>
Subject: selftests/bpf test_sockmap failure

In one of our production machines, tools/testing/selftests/bpf
test_sockmap failed randomly like below:

...
[TEST 78]: (512, 1, 1, sendmsg, pass,apply 1,): rx thread exited with 
err 1. FAILED
...

...
[TEST 80]: (2, 1024, 256, sendmsg, pass,apply 1,): rx thread exited with 
err 1. FAILED
...

...
[TEST 83]: (100, 1, 5, sendpage, pass,apply 1,): rx thread exited with 
err 1. FAILED
...

...
[TEST 79]: (512, 1, 1, sendpage, pass,apply 1,): rx thread exited with 
err 1. FAILED
...

The command line is just `test_sockmap`. The machine has 80 cpus, 256G 
memory. The kernel is based on 4.16 but backported with latest bpf-next 
bpf changes.

The failed test number (78, 79, 80, or 83) is random. But they all share
similar characteristics:
    . the option rate is greater than one, i.e., more than one
      sendmsg/sendpage in the sender forked process.
    . The txmsg_apply is not 0

I debugged a little bit. It happens in msg_loop() function below
"unexpected timeout" path.

...
                         slct = select(max_fd + 1, &w, NULL, NULL, 
&timeout);
                         if (slct == -1) {
                                 perror("select()");
                                 clock_gettime(CLOCK_MONOTONIC, &s->end);
                                 goto out_errno;
                         } else if (!slct) {
                                 if (opt->verbose)
                                         fprintf(stderr, "unexpected 
timeout\n");
                                 errno = -EIO;
                                 clock_gettime(CLOCK_MONOTONIC, &s->end);
                                 goto out_errno;
                         }
...

It appears that when the error happens, the receive process does not 
receive all bytes sent from the send process and eventually times out.

Has anybody seen this issue as well?
John, any comments on this failure?

Thanks,

Yonghong