[PATCH v3 4/9] rv/ha: fix ha_invariant_passed_ns silent bypass of invariant check

[wen.yang@linux.dev]

From: Wen Yang <wen.yang@linux.dev>

The function is documented as "prepare the invariant and return the time
since reset", but on the first call (env_store == U64_MAX) it exits
early without calling ha_set_invariant_ns():

  if (ha_monitor_env_invalid(ha_mon, env))  /* env_store == U64_MAX */
      return 0;   /* ha_set_invariant_ns skipped, env_store stays U64_MAX */
  ...
  ha_set_invariant_ns(ha_mon, env, expire - passed, time_ns);

This leaves env_store == U64_MAX, so ha_check_invariant_ns() always
passes on the first activation regardless of elapsed time:

  return READ_ONCE(ha_mon->env_store[env]) >= time_ns;  /* U64_MAX >= any */

Fix: establish the guard before converting to the invariant:

  if (ha_monitor_env_invalid(ha_mon, env))
      ha_reset_clk_ns(ha_mon, env, time_ns); /* guard: env_store = time_ns */
  passed = ha_get_env(ha_mon, env, time_ns);
  ha_set_invariant_ns(ha_mon, env, expire - passed, time_ns);
                                 /* invariant: env_store = time_ns + expire */

Apply the same fix to ha_invariant_passed_jiffy().

Signed-off-by: Wen Yang <wen.yang@linux.dev>
---
 include/rv/ha_monitor.h | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/include/rv/ha_monitor.h b/include/rv/ha_monitor.h
index 28d3c74cabfc..e5860900a337 100644
--- a/include/rv/ha_monitor.h
+++ b/include/rv/ha_monitor.h
@@ -365,16 +365,22 @@ static inline bool ha_check_invariant_ns(struct ha_monitor *ha_mon,
 }
 /*
  * ha_invariant_passed_ns - prepare the invariant and return the time since reset
+ *
+ * If the env has not been initialised yet (first entry into a state with an
+ * invariant), anchor the guard clock at the current time so that the full
+ * budget is available from this point.  This preserves the documented
+ * guard→invariant ordering: ha_set_invariant_ns() is always preceded by a
+ * valid guard representation in env_store.
  */
 static inline u64 ha_invariant_passed_ns(struct ha_monitor *ha_mon, enum envs env,
 				   u64 expire, u64 time_ns)
 {
-	u64 passed = 0;
+	u64 passed;
 
 	if (env < 0 || env >= ENV_MAX_STORED)
 		return 0;
 	if (ha_monitor_env_invalid(ha_mon, env))
-		return 0;
+		ha_reset_clk_ns(ha_mon, env, time_ns);
 	passed = ha_get_env(ha_mon, env, time_ns);
 	ha_set_invariant_ns(ha_mon, env, expire - passed, time_ns);
 	return passed;
@@ -404,16 +410,19 @@ static inline bool ha_check_invariant_jiffy(struct ha_monitor *ha_mon,
 }
 /*
  * ha_invariant_passed_jiffy - prepare the invariant and return the time since reset
+ *
+ * Same first-use semantics as ha_invariant_passed_ns(): anchor the guard clock
+ * now if the env has not been initialised.
  */
 static inline u64 ha_invariant_passed_jiffy(struct ha_monitor *ha_mon, enum envs env,
 				      u64 expire, u64 time_ns)
 {
-	u64 passed = 0;
+	u64 passed;
 
 	if (env < 0 || env >= ENV_MAX_STORED)
 		return 0;
 	if (ha_monitor_env_invalid(ha_mon, env))
-		return 0;
+		ha_reset_clk_jiffy(ha_mon, env);
 	passed = ha_get_env(ha_mon, env, time_ns);
 	ha_set_invariant_jiffy(ha_mon, env, expire - passed);
 	return passed;
-- 
2.43.0