Re: [PATCH v2] selftests/livepatch: better synchronize test_klp_callbacks_busy

[Petr Mladek <pmladek@suse.com>]

On Thu 2022-06-02 16:32:33, Joe Lawrence wrote:
> The test_klp_callbacks_busy module conditionally blocks a future
> livepatch transition by busy waiting inside its workqueue function,
> busymod_work_func().  After scheduling this work, a test livepatch is
> loaded, introducing the transition under test.
> 
> Both events are marked in the kernel log for later verification, but
> there is no synchronization to ensure that busymod_work_func() logs its
> function entry message before subsequent selftest commands log their own
> messages.  This can lead to a rare test failure due to unexpected
> ordering like:
> 
>   --- expected
>   +++ result
>   @@ -1,7 +1,7 @@
>    % modprobe test_klp_callbacks_busy block_transition=Y
>    test_klp_callbacks_busy: test_klp_callbacks_busy_init
>   -test_klp_callbacks_busy: busymod_work_func enter
>    % modprobe test_klp_callbacks_demo
>   +test_klp_callbacks_busy: busymod_work_func enter
>    livepatch: enabling patch 'test_klp_callbacks_demo'
>    livepatch: 'test_klp_callbacks_demo': initializing patching transition
>    test_klp_callbacks_demo: pre_patch_callback: vmlinux
> 
> Force the module init function to wait until busymod_work_func() has
> started (and logged its message), before exiting to the next selftest
> steps.
> 
> Fixes: 547840bd5ae5 ("selftests/livepatch: simplify test-klp-callbacks busy target tests")
> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
> Reviewed-by: Petr Mladek <pmladek@suse.com>

The patch has been committed into livepatching/livepatching.git,
branch for-5.20/selftests-fixes.

Best Regards,
Petr