Re: [PATCH] bpf: test_bpf: turn of preemption in function __run_once

On Thu, 21 Feb 2019 at 16:38, Daniel Borkmann [off-list ref] wrote:

On 02/21/2019 09:44 AM, Anders Roxell wrote:

quoted

When running test seccomp_bpf the following splat occurs:

[ RUN      ] global.secseccomp_bpf.c:2136:global.detect_seccomp_filter_flags:Expected 22 (22) == (*__errno_location ()) (14)
seccomp_bpf.c:2138:global.detect_seccomp_filter_flags:Failed to detect that an unknown
  filter flag (0x8) is unsupported! Does a new flag need to be added to this test?
[ 2155.677841] BUG: assuming atomic context at kernel/seccomp.c:271
[ 2155.689351] in_atomic(): 0, irqs_disabled(): 0, pid: 28540, name: seccomp_bpf
[ 2155.696597] INFO: lockdep is turned off.
[ 2155.700605] CPU: 5 PID: 28540 Comm: seccomp_bpf Tainted: G        W         5.0.0-rc7-next-20190220 #1
[ 2155.709972] Hardware name: HiKey Development Board (DT)
[ 2155.715232] Call trace:
[ 2155.717710]  dump_backtrace+0x0/0x160
[ 2155.721399]  show_stack+0x24/0x30
[ 2155.724742]  dump_stack+0xc8/0x114
[ 2155.728172]  __cant_sleep+0xf0/0x108
[ 2155.731777]  __seccomp_filter+0x8c/0x5c8
[ 2155.735727]  __secure_computing+0x4c/0xe8
[ 2155.739767]  syscall_trace_enter+0xf8/0x2b8
[ 2155.743982]  el0_svc_common+0xf0/0x130
[ 2155.747758]  el0_svc_handler+0x38/0x78
[ 2155.751534]  el0_svc+0x8/0xc

Rework so that preemption is disabled when we loop over function
'BPF_PROG_RUN(...)'.
Commit 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
highlighted the issue.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <redacted>

Hmm, wrong commit description?

urgh, you are correct. I'm sorry.
Sending a v2 shortly.

Below code is not related to seccomp
but rather BPF test suite. Could you fix it up and resubmit? Rest
looks okay to me.

quoted

---
 lib/test_bpf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index f3e570722a7e..0845f635f404 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c

@@ -6668,12 +6668,14 @@ static int __run_one(const struct bpf_prog *fp, const void *data,
      u64 start, finish;
      int ret = 0, i;

+     preempt_disable();
      start = ktime_get_ns();

      for (i = 0; i < runs; i++)
              ret = BPF_PROG_RUN(fp, data);

      finish = ktime_get_ns();
+     preempt_enable();

      *duration = finish - start;
      do_div(*duration, runs);