* [PATCH v2] selftests/livepatch: better synchronize test_klp_callbacks_busy
@ 2022-06-02 20:32 Joe Lawrence
2022-06-15 9:21 ` Petr Mladek
0 siblings, 1 reply; 2+ messages in thread
From: Joe Lawrence @ 2022-06-02 20:32 UTC (permalink / raw)
To: live-patching; +Cc: Joe Lawrence, Miroslav Benes, Petr Mladek, Yannick Cote
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>
---
lib/livepatch/test_klp_callbacks_busy.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/lib/livepatch/test_klp_callbacks_busy.c b/lib/livepatch/test_klp_callbacks_busy.c
index 7ac845f65be5..133929e0ce8f 100644
--- 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, "block_transition (default=false)");
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(void)
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
--
2.26.3
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] selftests/livepatch: better synchronize test_klp_callbacks_busy
2022-06-02 20:32 [PATCH v2] selftests/livepatch: better synchronize test_klp_callbacks_busy Joe Lawrence
@ 2022-06-15 9:21 ` Petr Mladek
0 siblings, 0 replies; 2+ messages in thread
From: Petr Mladek @ 2022-06-15 9:21 UTC (permalink / raw)
To: Joe Lawrence; +Cc: live-patching, Miroslav Benes, Yannick Cote
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
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