From: Joe Lawrence joe.lawrence@redhat.com
[ Upstream commit 55eb9a6c8bf3e2099863118ef53e02d9f44f85a8 ]
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 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 --- lib/livepatch/test_klp_callbacks_busy.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/lib/livepatch/test_klp_callbacks_busy.c +++ b/lib/livepatch/test_klp_callbacks_busy.c @@ -16,10 +16,12 @@ MODULE_PARM_DESC(block_transition, "bloc
static void busymod_work_func(struct work_struct *work); static DECLARE_WORK(work, busymod_work_func); +static DECLARE_COMPLETION(busymod_work_started);
static void busymod_work_func(struct work_struct *work) { pr_info("%s enter\n", __func__); + complete(&busymod_work_started);
while (READ_ONCE(block_transition)) { /* @@ -37,6 +39,12 @@ static int test_klp_callbacks_busy_init( pr_info("%s\n", __func__); schedule_work(&work);
+ /* + * To synchronize kernel messages, hold the init function from + * exiting until the work function's entry message has printed. + */ + wait_for_completion(&busymod_work_started); + if (!block_transition) { /* * Serialize output: print all messages from the work