On 7/6/26 22:41, Gabriele Monaco wrote:
On Tue, 2026-06-16 at 00:44 +0800, [email protected] wrote:
From: Wen Yang <[email protected]>
Add KUnit tests for the printk reactor covering:
- Reactor registration and unregistration lifecycle
- React callback invocation via rv_react()
- Double registration rejection
- Multiple register/unregister cycles
The mock callback calls vprintk_deferred() — the same path as the real
reactor — then busy-waits to simulate I/O back-pressure, exercising the
LD_WAIT_FREE constraint of rv_react() under load.
Signed-off-by: Wen Yang <[email protected]>
---
kernel/trace/rv/Kconfig | 10 ++
kernel/trace/rv/Makefile | 1 +
kernel/trace/rv/reactor_printk_kunit.c | 123 +++++++++++++++++++++++++
3 files changed, 134 insertions(+)
create mode 100644 kernel/trace/rv/reactor_printk_kunit.c
diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index 3884b14df375..ff47895c897f 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -104,6 +104,16 @@ config RV_REACT_PRINTK
Enables the printk reactor. The printk reactor emits a printk()
message if an exception is found.
+config RV_REACT_PRINTK_KUNIT
+ bool "KUnit tests for reactor_printk" if !KUNIT_ALL_TESTS
+ depends on RV_REACT_PRINTK && KUNIT
+ default KUNIT_ALL_TESTS
+ help
+ This builds KUnit tests for the printk reactor. These are only
+ for development and testing, not for regular kernel use cases.
+
+ If unsure, say N.
+
config RV_REACT_PANIC
bool "Panic reactor"
depends on RV_REACTORS
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index 94498da35b37..ef0a2dcb927c 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -23,4 +23,5 @@ obj-$(CONFIG_RV_MON_NOMISS) += monitors/nomiss/nomiss.o
# Add new monitors here
obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o
+obj-$(CONFIG_RV_REACT_PRINTK_KUNIT) += reactor_printk_kunit.o
obj-$(CONFIG_RV_REACT_PANIC) += reactor_panic.o
diff --git a/kernel/trace/rv/reactor_printk_kunit.c
b/kernel/trace/rv/reactor_printk_kunit.c
new file mode 100644
index 000000000000..933aa5602226
--- /dev/null
+++ b/kernel/trace/rv/reactor_printk_kunit.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for reactor_printk
+ *
+ */
+
+#include <kunit/test.h>
+#include <linux/rv.h>
+#include <linux/printk.h>
+#include <linux/sched/clock.h>
+#include <linux/processor.h>
+
+/*
+ * Simulated execution time for mock_printk_react (sched_clock units,
+ * nanoseconds). Models the time a real printk reactor callback may consume
+ * under I/O pressure, exercising the LD_WAIT_FREE constraint of rv_react().
+ */
+#define MOCK_REACT_DURATION_NS 5000000ULL
+
+/*
+ * Mock react callback mirroring rv_printk_reaction().
+ *
+ * Calls vprintk_deferred() — the same path as the real reactor — then holds
+ * the CPU for MOCK_REACT_DURATION_NS via a sched_clock() timed busy-loop,
+ * simulating a callback that is slow due to I/O back-pressure.
+ * sched_clock() is notrace and lock-free; no sleep or lock acquisition is
+ * performed, satisfying the LD_WAIT_FREE constraint of rv_react().
+ */
+__printf(1, 0) static void mock_printk_react(const char *msg, va_list args)
+{
+ u64 start = sched_clock();
+
I'm fine testing something that looks like the printk reactor rather than the
real thing, but here sched_clock() is playing with preemption and could trigger
one, this isn't accurate.
I'm not sure all implementations are free from this problem, but why don't you
just use mdelay() here?
Thanks,
v2 uses mdelay(5) for the busy-wait. The goal is simply to hold the CPU
inside rv_react()'s lockdep context; so mdelay() is a pure calibrated
spin with no scheduler interaction, making the test's causal chain
clearer than sched_clock().
The remaining comments are also very important, and we will address them
in v2.
--
Best wishes,
Wen
