Date: Mon, 3 Jun 2024 14:52:45 +0200
From: Petr Mladek <pmladek@...e.com>
To: Marcos Paulo de Souza <mpdesouza@...e.com>
Cc: Joe Lawrence <joe.lawrence@...hat.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
	Shuah Khan <shuah@...nel.org>, live-patching@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] selftests: livepatch: Test atomic replace against
 multiple modules

On Fri 2024-05-31 18:06:48, Marcos Paulo de Souza wrote:
> On Fri, 2024-05-31 at 15:44 -0400, Joe Lawrence wrote:
> > On Sat, May 25, 2024 at 11:34:08AM -0300, Marcos Paulo de Souza
> > wrote:
> > > Adapt the current test-livepatch.sh script to account the number of
> > > applied livepatches and ensure that an atomic replace livepatch
> > > disables
> > > all previously applied livepatches.
> > > 
> > > Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>
> > > ---
> > > Changes since v1:
> > > * Added checks in the existing test-livepatch.sh instead of
> > > creating a
> > >   new test file. (Joe)
> > > * Fixed issues reported by ShellCheck (Joe)
> > > ---
> > >  .../testing/selftests/livepatch/test-livepatch.sh  | 46
> > > ++++++++++++++++++++--
> > >  1 file changed, 42 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/tools/testing/selftests/livepatch/test-livepatch.sh
> > > b/tools/testing/selftests/livepatch/test-livepatch.sh
> > > index e3455a6b1158..d85405d18e54 100755
> > > --- a/tools/testing/selftests/livepatch/test-livepatch.sh
> > > +++ b/tools/testing/selftests/livepatch/test-livepatch.sh
> > > @@ -107,9 +107,12 @@ livepatch: '$MOD_LIVEPATCH': unpatching
> > > complete
> > >  
> > >  # - load a livepatch that modifies the output from /proc/cmdline
> > > and
> > >  #   verify correct behavior
> > > -# - load an atomic replace livepatch and verify that only the
> > > second is active
> > > -# - remove the first livepatch and verify that the atomic replace
> > > livepatch
> > > -#   is still active
> > > +# - load two addtional livepatches and check the number of
> > > livepatch modules
> > > +#   applied
> > > +# - load an atomic replace livepatch and check that the other
> > > three modules were
> > > +#   disabled
> > > +# - remove all livepatches besides the atomic replace one and
> > > verify that the
> > > +#   atomic replace livepatch is still active
> > >  # - remove the atomic replace livepatch and verify that none are
> > > active
> > >  
> > >  start_test "atomic replace livepatch"
> > > @@ -119,12 +122,31 @@ load_lp $MOD_LIVEPATCH
> > >  grep 'live patched' /proc/cmdline > /dev/kmsg
> > >  grep 'live patched' /proc/meminfo > /dev/kmsg
> > >  
> > > +for mod in test_klp_syscall test_klp_callbacks_demo; do
> > 
> > Slightly nitpicky here, but the tests were originally written with
> > the
> > livepatch module names via variables like $MOD_LIVEPATCH.  Would
> > using
> > $MOD_LIVEPATCH{1,2,3} help indicate that their specifics aren't
> > really
> > interesting, that we just need 3 of them?
> 
> Makes sense. I thought about it when I was changing the code, but I
> didn't want to change it too much, so it was the result. But that makes
> sense to have the modules better named.

I like this.

> > > +	load_lp $mod
> > > +done
> > > +
> > > +mods=(/sys/kernel/livepatch/*)
> > > +nmods=${#mods[@]}
> > > +if [ "$nmods" -ne 3 ]; then
> > > +	die "Expecting three modules listed, found $nmods"
> > > +fi
> > > +
> > 
> > I was going to suggest that we might protect against a situation
> > where
> > other livepatch modules were active, that a simple count wouldn't be
> > sufficient.  But then I thought about this test, atomic replace!
> > Anything previously loaded is going to be pushed aside anyway.
> > 
> > So maybe (in another patch or set) it would be worth enhancing
> > functions.sh :: start_test() do a quick sanity check to see that the
> > initial conditions are safe?  That might also prevent some collateral
> > damage when test A fails and leaves the world a strange place for
> > tests
> > B, C, etc.
> 
> We have been discussing about start/end functions that would check for
> leftover modules... maybe should be a good think to implement soon as
> we land more tests.

Makes sense :-)

> > >  load_lp $MOD_REPLACE replace=1
> > >  
> > >  grep 'live patched' /proc/cmdline > /dev/kmsg
> > >  grep 'live patched' /proc/meminfo > /dev/kmsg
> > >  
> > > -unload_lp $MOD_LIVEPATCH
> > > +mods=(/sys/kernel/livepatch/*)
> > > +nmods=${#mods[@]}
> > > +if [ "$nmods" -ne 1 ]; then
> > > +	die "Expecting only one moduled listed, found $nmods"
> > > +fi
> > > +
> > > +# These modules were disabled by the atomic replace
> > > +for mod in test_klp_callbacks_demo test_klp_syscall
> > > $MOD_LIVEPATCH; do
> > > +	unload_lp "$mod"
> > > +done
> > >  
> > >  grep 'live patched' /proc/cmdline > /dev/kmsg
> > >  grep 'live patched' /proc/meminfo > /dev/kmsg
> > > @@ -142,6 +164,20 @@ livepatch: '$MOD_LIVEPATCH': starting patching
> > > transition
> > >  livepatch: '$MOD_LIVEPATCH': completing patching transition
> > >  livepatch: '$MOD_LIVEPATCH': patching complete
> > >  $MOD_LIVEPATCH: this has been live patched
> > > +% insmod test_modules/test_klp_syscall.ko
> > 
> > Similar minor nit here, too.  If we think copy/pasting all the
> > $MOD_FOO
> > is annoying, I am fine with leaving this as is.  I don't have a
> > strong
> > opinion other than following some convention.
> > 
> > With that, I'm happy to ack as-is or with variable names.
> 
> Thanks Joe! I think that is Petr's call, either way I can rework this
> patch, or send additional ones to adjust the tests.

I would prefer if you did respin this patch. The use of
$MOD_LIVEPATCH{1,2,3} would make even the patch easier to follow.

Best Regards,
Petr

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