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Date:   Fri, 18 Feb 2022 09:54:26 +0100 (CET)
From:   Miroslav Benes <mbenes@suse.cz>
To:     David Vernet <void@manifault.com>
cc:     live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
        jpoimboe@redhat.com, pmladek@suse.com, jikos@kernel.org,
        joe.lawrence@redhat.com, corbet@lwn.net, kernel-team@fb.com
Subject: Re: [PATCH v3] livepatch: Skip livepatch tests if ftrace cannot be
 configured
In-Reply-To: <20220216161100.3243100-1-void@manifault.com>
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References: <20220216161100.3243100-1-void@manifault.com>
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On Wed, 16 Feb 2022, 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 updates set_ftrace_enabled() to detect sysctl failures,
> and skip the testrun when appropriate.
> 
> Suggested-by: Petr Mladek <pmladek@suse.com>
> Signed-off-by: David Vernet <void@manifault.com>

Acked-by: Miroslav Benes <mbenes@suse.cz>

M