selftests/livepatch: better synchronize test_klp_callbacks_busy

stable inclusion
from stable-v5.10.137
commit 3bf64b9cc640b5bb2b4c13176d59b28b8b987dae
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3bf64b9cc640b5bb2b4c13176d59b28b8b987dae



--------------------------------

[ Upstream commit 55eb9a6c ]

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: 547840bd ("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>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220602203233.979681-1-joe.lawrence@redhat.com


Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>