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

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Message-ID: <alpine.LSU.2.21.1910151259220.30206@pobox.suse.cz>
Date:   Tue, 15 Oct 2019 13:23:10 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Joe Lawrence <joe.lawrence@...hat.com>
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

> 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.

> +function pop_ftrace_enabled() {
> +	if [[ -n "$FTRACE_ENABLED" ]]; then
> +		sysctl kernel.ftrace_enabled="$FTRACE_ENABLED"
> +	fi
> +}
> +# set_ftrace_enabled() - save the current ftrace_enabled config and tweak
> +# 			 it for the self-tests.  Set a script exit trap
> +#			 that restores the original value.
> +function set_ftrace_enabled() {
> +	local sysctl="$1"
> +        trap pop_ftrace_enabled EXIT INT TERM HUP
> +	result=$(sysctl kernel.ftrace_enabled="$1" 2>&1 | paste --serial --delimiters=' ')
> +	echo "livepatch: $result" > /dev/kmsg
> +}
> +
>  # loop_until(cmd) - loop a command until it is successful or $MAX_RETRIES,
>  #		    sleep $RETRY_INTERVAL between attempts
>  #	cmd - command and its arguments to run

Miroslav