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Date:   Mon, 16 Mar 2020 22:39:40 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [Potential Spoof] [PATCH bpf-next 3/3] selftests/bpf: reset
 process and thread affinity after each test/sub-test

On Mon, Mar 16, 2020 at 10:35 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Fri, Mar 13, 2020 at 06:39:32PM -0700, Andrii Nakryiko wrote:
> > Some tests and sub-tests are setting "custom" thread/process affinity and
> > don't reset it back. Instead of requiring each test to undo all this, ensure
> > that thread affinity is restored by test_progs test runner itself.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> >  tools/testing/selftests/bpf/test_progs.c | 42 +++++++++++++++++++++++-
> >  tools/testing/selftests/bpf/test_progs.h |  1 +
> >  2 files changed, 42 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> > index c8cb407482c6..b521e0a512b6 100644
> > --- a/tools/testing/selftests/bpf/test_progs.c
> > +++ b/tools/testing/selftests/bpf/test_progs.c
> > @@ -1,12 +1,15 @@
> >  // SPDX-License-Identifier: GPL-2.0-only
> >  /* Copyright (c) 2017 Facebook
> >   */
> > +#define _GNU_SOURCE
> >  #include "test_progs.h"
> >  #include "cgroup_helpers.h"
> >  #include "bpf_rlimit.h"
> >  #include <argp.h>
> > -#include <string.h>
> > +#include <pthread.h>
> > +#include <sched.h>
> >  #include <signal.h>
> > +#include <string.h>
> >  #include <execinfo.h> /* backtrace */
> >
> >  /* defined in test_progs.h */
> > @@ -90,6 +93,34 @@ static void skip_account(void)
> >       }
> >  }
> >
> > +static void stdio_restore(void);
> > +
> > +/* A bunch of tests set custom affinity per-thread and/or per-process. Reset
> > + * it after each test/sub-test.
> > + */
> > +static void reset_affinity() {
> > +
> > +     cpu_set_t cpuset;
> > +     int i, err;
> > +
> > +     CPU_ZERO(&cpuset);
> > +     for (i = 0; i < env.nr_cpus; i++)
> > +             CPU_SET(i, &cpuset);
> In case the user may run "taskset somemask test_progs",
> is it better to store the inital_cpuset at the beginning
> of main and then restore to inital_cpuset after each run?

Not sure it's worth it (it's test runner, not really a general-purpose
tool), but I can add that for sure.

>
> > +
> > +     err = sched_setaffinity(0, sizeof(cpuset), &cpuset);
> > +     if (err < 0) {
> > +             stdio_restore();
> > +             fprintf(stderr, "Failed to reset process affinity: %d!\n", err);
> > +             exit(-1);
> > +     }
> > +     err = pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);
> > +     if (err < 0) {
> > +             stdio_restore();
> > +             fprintf(stderr, "Failed to reset thread affinity: %d!\n", err);
> > +             exit(-1);
> > +     }
> > +}

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