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 [off-list ref] wrote:

On Fri, Mar 13, 2020 at 06:39:32PM -0700, Andrii Nakryiko wrote:

quoted

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 <redacted>
---
 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.

quoted

+
+     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);
+     }
+}