From: Joe Lawrence <joe.lawrence@redhat.com>
To: David Vernet <void@manifault.com>,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
jpoimboe@redhat.com, pmladek@suse.com, jikos@kernel.org,
mbenes@suse.cz, corbet@lwn.net
Cc: kernel-team@fb.com
Subject: Re: [PATCH v2] livepatch: Skip livepatch tests if ftrace cannot be configured
Date: Tue, 8 Feb 2022 10:45:02 -0500 [thread overview]
Message-ID: <89a430e9-6da4-761a-68aa-187a3faa9c53@redhat.com> (raw)
In-Reply-To: <20220204205625.2628328-1-void@manifault.com>
On 2/4/22 3:56 PM, David Vernet wrote:
> livepatch has a set of selftests that are used to validate the behavior of
> the livepatching subsystem. One of the testcases in the livepatch
> testsuite is test-ftrace.sh, which among other things, validates that
> livepatching gracefully fails when ftrace is disabled. In the event that
> ftrace cannot be disabled using 'sysctl kernel.ftrace_enabled=0', the test
> will fail later due to it unexpectedly successfully loading the
> test_klp_livepatch module.
>
> While the livepatch selftests are careful to remove any of the livepatch
> test modules between testcases to avoid this situation, ftrace may still
> fail to be disabled if another trace is active on the system that was
> enabled with FTRACE_OPS_FL_PERMANENT. For example, any active BPF programs
> that use trampolines will cause this test to fail due to the trampoline
> being implemented with register_ftrace_direct(). The following is an
> example of such a trace:
>
> tcp_drop (1) R I D tramp: ftrace_regs_caller+0x0/0x58
> (call_direct_funcs+0x0/0x30)
> direct-->bpf_trampoline_6442550536_0+0x0/0x1000
>
> In order to make the test more resilient to system state that is out of its
> control, this patch adds a check to set_ftrace_enabled() to skip the tests
> if the sysctl invocation fails.
>
> Signed-off-by: David Vernet <void@manifault.com>
> ---
> v2:
> - Fix typo in newly added comment (s/permament/permanent).
> - Adjust the location of the added newline to be before the new comment
> rather than that the end of the function.
> - Make the failure-path check a bit less brittle by checking for the
> exact expected string, rather than specifically for "Device or resource
> busy".
>
> tools/testing/selftests/livepatch/functions.sh | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
> index 846c7ed71556..32970324dd7e 100644
> --- a/tools/testing/selftests/livepatch/functions.sh
> +++ b/tools/testing/selftests/livepatch/functions.sh
> @@ -78,6 +78,12 @@ function set_ftrace_enabled() {
> result=$(sysctl -q kernel.ftrace_enabled="$1" 2>&1 && \
> sysctl kernel.ftrace_enabled 2>&1)
> echo "livepatch: $result" > /dev/kmsg
> +
> + # Skip the test if ftrace is busy. This can happen under normal system
> + # conditions if a trace is marked as permanent.
> + if [[ "$result" != "kernel.ftrace_enabled = $1" ]]; then
> + skip "failed to set kernel.ftrace_enabled=$1"
> + fi
> }
>
> function cleanup() {
>
Thanks for updating.
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
--
Joe
next prev parent reply other threads:[~2022-02-08 15:45 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-03 23:32 [PATCH] livepatch: Skip livepatch tests if ftrace cannot be configured David Vernet
2022-02-04 20:30 ` Joe Lawrence
2022-02-04 20:43 ` David Vernet
2022-02-04 20:56 ` [PATCH v2] " David Vernet
2022-02-08 15:45 ` Joe Lawrence [this message]
2022-02-09 13:02 ` Petr Mladek
2022-02-09 15:49 ` David Vernet
2022-02-10 15:23 ` Petr Mladek
2022-02-10 16:22 ` David Vernet
2022-02-10 20:58 ` Joe Lawrence
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