netdev - Re: [PATCH] bpf: test_bpf: turn of preemption in function __run

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Date:   Fri, 22 Feb 2019 09:25:32 +0100
From:   Anders Roxell <anders.roxell@...aro.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: test_bpf: turn of preemption in function __run_once

On Thu, 21 Feb 2019 at 16:38, Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 02/21/2019 09:44 AM, Anders Roxell wrote:
> > 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@...db.de>
> > Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
>
> 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.
>
> > ---
> >  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);
> >
>