[PATCH v2 1/2] hrtimer: Add cleanup class for on-stack timers

[Hui Su]

hrtimer_setup_on_stack() requires callers to destroy the timer before its
backing stack storage goes out of scope, but the setup interface does not
encode the required teardown pairing.

Add an hrtimer_on_stack cleanup class that pairs on-stack setup with
destroy_hrtimer_on_stack(). Document the existing setup API's lifetime
requirement.

The cleanup class provides debug-object teardown, not timer
cancellation. Callers must ensure that no hrtimer operation can still
access the timer before the scope ends; in particular, the timer must
no longer be queued and any running callback must have completed.

Signed-off-by: Hui Su <sh_def@xxxxxxx>
---
 include/linux/hrtimer.h | 24 ++++++++++++++++++++++++
 kernel/time/hrtimer.c   |  8 ++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 29072d89e5cb..1877beb81d5c 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -12,6 +12,7 @@
 #ifndef _LINUX_HRTIMER_H
 #define _LINUX_HRTIMER_H
 
+#include <linux/cleanup.h>
 #include <linux/hrtimer_rearm.h>
 #include <linux/hrtimer_types.h>
 #include <linux/init.h>
@@ -201,6 +202,29 @@ extern void destroy_hrtimer_on_stack(struct hrtimer *timer);
 static inline void destroy_hrtimer_on_stack(struct hrtimer *timer) { }
 #endif
 
+/*
+ * The cleanup class pairs on-stack setup with debug-object teardown. Callers
+ * using it must not call destroy_hrtimer_on_stack() manually.
+ *
+ * This class provides debug-object teardown, not timer cancellation. Callers
+ * must ensure that no hrtimer operation can still access the timer before
+ * leaving the scope. In particular, the timer must no longer be queued and
+ * any running callback must have completed.
+ *
+ * Callers using hrtimer_setup_on_stack() without this class retain
+ * responsibility for destroying the timer before its backing storage leaves
+ * scope.
+ */
+DEFINE_CLASS(hrtimer_on_stack, struct hrtimer *,
+	     destroy_hrtimer_on_stack(_T),
+	     ({
+		hrtimer_setup_on_stack(timer, function, clock_id, mode);
+		timer;
+	     }),
+	     struct hrtimer *timer,
+	     enum hrtimer_restart (*function)(struct hrtimer *),
+	     clockid_t clock_id, enum hrtimer_mode mode)
+
 /* Basic timer operations: */
 extern void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 				   u64 range_ns, const enum hrtimer_mode mode);
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index cbf1693c86b3..12e136d5691f 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1975,8 +1975,12 @@ EXPORT_SYMBOL_GPL(hrtimer_setup);
  * @clock_id:	The clock to be used
  * @mode:       The timer mode
  *
- * Similar to hrtimer_setup(), except that this one must be used if struct hrtimer is in stack
- * memory.
+ * Similar to hrtimer_setup(), except that this one must be used if struct
+ * hrtimer is in stack memory.
+ *
+ * Callers that do not use the hrtimer_on_stack cleanup class must call
+ * destroy_hrtimer_on_stack() before the stack storage goes out of scope. The
+ * cleanup class pairs setup and destruction automatically.
  */
 void hrtimer_setup_on_stack(struct hrtimer *timer,
 			    enum hrtimer_restart (*function)(struct hrtimer *),
-- 
2.55.0