[PATCH 4/9] rv: Prevent task migration while handling per-CPU events

[Gabriele Monaco <gmonaco@redhat.com>]

Tracepoint handlers are now fully preemptible. When a per-CPU monitor
handles an event, it retrieves the monitor state using a per-CPU
pointer. If the event itself doesn't disable preemption, the task can
migrate to a different CPU and we risk updating the wrong monitor.

Mitigate this by explicitly disabling task migration before acquiring
the monitor pointer. This cannot guarantee the monitor runs on the
correct CPU but reduces the race condition window and prevents warnings.

Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
---
 include/rv/da_monitor.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h
index 0b7028df08fb..a9fd284195ee 100644
--- a/include/rv/da_monitor.h
+++ b/include/rv/da_monitor.h
@@ -181,6 +181,10 @@ static inline void da_monitor_destroy(void)
 	da_monitor_reset_all();
 }
 
+#ifndef da_implicit_guard
+#define da_implicit_guard()
+#endif
+
 #elif RV_MON_TYPE == RV_MON_PER_CPU
 /*
  * Functions to define, init and get a per-cpu monitor.
@@ -230,6 +234,10 @@ static inline void da_monitor_destroy(void)
 	da_monitor_reset_all();
 }
 
+#ifndef da_implicit_guard
+#define da_implicit_guard() guard(migrate)()
+#endif
+
 #elif RV_MON_TYPE == RV_MON_PER_TASK
 /*
  * Functions to define, init and get a per-task monitor.
@@ -677,6 +685,7 @@ static inline bool __da_handle_start_run_event(struct da_monitor *da_mon,
  */
 static inline void da_handle_event(enum events event)
 {
+	da_implicit_guard();
 	__da_handle_event(da_get_monitor(), event, 0);
 }
 
@@ -692,6 +701,7 @@ static inline void da_handle_event(enum events event)
  */
 static inline bool da_handle_start_event(enum events event)
 {
+	da_implicit_guard();
 	return __da_handle_start_event(da_get_monitor(), event, 0);
 }
 
@@ -703,6 +713,7 @@ static inline bool da_handle_start_event(enum events event)
  */
 static inline bool da_handle_start_run_event(enum events event)
 {
+	da_implicit_guard();
 	return __da_handle_start_run_event(da_get_monitor(), event, 0);
 }
 
-- 
2.54.0