linux-kernel - Re: [PATCH v2] ftrace: Introduce PERMANENT ftrace

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Date:   Tue, 15 Oct 2019 09:25:45 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     rostedt@...dmis.org, mingo@...hat.com, jpoimboe@...hat.com,
        jikos@...nel.org, pmladek@...e.com, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org
Subject: Re: [PATCH v2] ftrace: Introduce PERMANENT ftrace_ops flag

On 10/15/19 7:23 AM, Miroslav Benes wrote:
>> Hi Miroslav,
>>
>> Maybe we should add a test to verify this new behavior?  See sample
>> version below (lightly tested).  We can add to this one, or patch
>> seperately if you prefer.
> 
> Thanks a lot, Joe. It looks nice. I'll include it in v3. One question
> below.
>   
>> -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8--
>>
>>   
>> >From c8c9f22e3816ca4c90ab7e7159d2ce536eaa5fad Mon Sep 17 00:00:00 2001
>> From: Joe Lawrence <joe.lawrence@...hat.com>
>> Date: Mon, 14 Oct 2019 18:25:01 -0400
>> Subject: [PATCH] selftests/livepatch: test interaction with ftrace_enabled
>>
>> Since livepatching depends upon ftrace handlers to implement "patched"
>> functionality, verify that the ftrace_enabled sysctl value interacts
>> with livepatch registration as expected.
>>
>> Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
>> ---
>>   tools/testing/selftests/livepatch/Makefile    |  3 +-
>>   .../testing/selftests/livepatch/functions.sh  | 18 +++++
>>   .../selftests/livepatch/test-ftrace.sh        | 65 +++++++++++++++++++
>>   3 files changed, 85 insertions(+), 1 deletion(-)
>>   create mode 100755 tools/testing/selftests/livepatch/test-ftrace.sh
>>
>> diff --git a/tools/testing/selftests/livepatch/Makefile b/tools/testing/selftests/livepatch/Makefile
>> index fd405402c3ff..1886d9d94b88 100644
>> --- a/tools/testing/selftests/livepatch/Makefile
>> +++ b/tools/testing/selftests/livepatch/Makefile
>> @@ -4,6 +4,7 @@ TEST_PROGS_EXTENDED := functions.sh
>>   TEST_PROGS := \
>>   	test-livepatch.sh \
>>   	test-callbacks.sh \
>> -	test-shadow-vars.sh
>> +	test-shadow-vars.sh \
>> +	test-ftrace.sh
>>   
>>   include ../lib.mk
>> diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
>> index 79b0affd21fb..556252efece0 100644
>> --- a/tools/testing/selftests/livepatch/functions.sh
>> +++ b/tools/testing/selftests/livepatch/functions.sh
>> @@ -52,6 +52,24 @@ function set_dynamic_debug() {
>>   		EOF
>>   }
>>   
>> +function push_ftrace_enabled() {
>> +	FTRACE_ENABLED=$(sysctl --values kernel.ftrace_enabled)
>> +}
> 
> Shouldn't we call push_ftrace_enabled() somewhere at the beginning of the
> test script? set_dynamic_debug() calls its push_dynamic_debug() directly,
> but set_ftrace_enabled() is different, because it is called more than once
> in the script.
> 
> One could argue that ftrace_enabled has to be true at the beginning of
> testing anyway, but I think it would be cleaner. Btw, we should probably
> guarantee that ftrace_enabled is true when livepatch selftests are
> invoked.
> 

Ah yes, that occurred to me while creating that piece of the patch. 
Something like setup_test_config() that pushes both ftrace and the 
debugfs, etc. would be cleaner for all scripts.  If you're onboard with 
that idea, I can make that revision.

-- Joe