netdev - [PATCH AUTOSEL 5.19 071/105] selftests/bpf: Do not attach kprobe_multi bench to bpf_dispatcher_xdp

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Date:   Thu, 11 Aug 2022 11:27:55 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Yonghong Song <yhs@...com>, Sasha Levin <sashal@...nel.org>,
        daniel@...earbox.net, shuah@...nel.org, davem@...emloft.net,
        kuba@...nel.org, hawk@...nel.org, john.fastabend@...il.com,
        bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
        netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.19 071/105] selftests/bpf: Do not attach kprobe_multi bench to bpf_dispatcher_xdp_func

From: Jiri Olsa <jolsa@...nel.org>

[ Upstream commit 7fb27a56b9ebd8a77d9dd188e8a42bff99bc3443 ]

Alexei reported crash by running test_progs -j on system
with 32 cpus.

It turned out the kprobe_multi bench test that attaches all
ftrace-able functions will race with bpf_dispatcher_update,
that calls bpf_arch_text_poke on bpf_dispatcher_xdp_func,
which is ftrace-able function.

Ftrace is not aware of this update so this will cause
ftrace_bug with:

  WARNING: CPU: 6 PID: 1985 at
  arch/x86/kernel/ftrace.c:94 ftrace_verify_code+0x27/0x50
  ...
  ftrace_replace_code+0xa3/0x170
  ftrace_modify_all_code+0xbd/0x150
  ftrace_startup_enable+0x3f/0x50
  ftrace_startup+0x98/0xf0
  register_ftrace_function+0x20/0x60
  register_fprobe_ips+0xbb/0xd0
  bpf_kprobe_multi_link_attach+0x179/0x430
  __sys_bpf+0x18a1/0x2440
  ...
  ------------[ ftrace bug ]------------
  ftrace failed to modify
  [<ffffffff818d9380>] bpf_dispatcher_xdp_func+0x0/0x10
   actual:   ffffffe9:7b:ffffff9c:77:1e
  Setting ftrace call site to call ftrace function

It looks like we need some way to hide some functions
from ftrace, but meanwhile we workaround this by skipping
bpf_dispatcher_xdp_func from kprobe_multi bench test.

Reported-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Acked-by: Yonghong Song <yhs@...com>
Link: https://lore.kernel.org/bpf/20220714082316.479181-1-jolsa@kernel.org
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
index 5b93d5d0bd93..48681bf73e0b 100644
--- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
@@ -364,6 +364,8 @@ static int get_syms(char ***symsp, size_t *cntp)
 			continue;
 		if (!strncmp(name, "rcu_", 4))
 			continue;
+		if (!strcmp(name, "bpf_dispatcher_xdp_func"))
+			continue;
 		if (!strncmp(name, "__ftrace_invalid_address__",
 			     sizeof("__ftrace_invalid_address__") - 1))
 			continue;
-- 
2.35.1