MFp4:

It is possible a lower priority thread lending priority to higher priority
thread, in old code, it is ignored, however the lending should always be
recorded, add field td_lend_user_pri to fix the problem, if a thread does
not have borrowed priority, its value is PRI_MAX.

MFC after: 1 week

1 files changed, 10 insertions, 13 deletions

diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c
index 9face64..6278126 100644
--- a/sys/kern/sched_4bsd.c
+++ b/sys/kern/sched_4bsd.c
@@ -879,25 +879,23 @@ sched_prio(struct thread *td, u_char prio)
 void
 sched_user_prio(struct thread *td, u_char prio)
 {
-	u_char oldprio;
 
 	THREAD_LOCK_ASSERT(td, MA_OWNED);
 	td->td_base_user_pri = prio;
-	if (td->td_flags & TDF_UBORROWING && td->td_user_pri <= prio)
+	if (td->td_lend_user_pri <= prio)
 		return;
-	oldprio = td->td_user_pri;
 	td->td_user_pri = prio;
 }
 
 void
 sched_lend_user_prio(struct thread *td, u_char prio)
 {
-	u_char oldprio;
 
 	THREAD_LOCK_ASSERT(td, MA_OWNED);
-	td->td_flags |= TDF_UBORROWING;
-	oldprio = td->td_user_pri;
-	td->td_user_pri = prio;
+	if (prio < td->td_lend_user_pri)
+		td->td_lend_user_pri = prio;
+	if (prio < td->td_user_pri)
+		td->td_user_pri = prio;
 }
 
 void
@@ -907,12 +905,11 @@ sched_unlend_user_prio(struct thread *td, u_char prio)
 
 	THREAD_LOCK_ASSERT(td, MA_OWNED);
 	base_pri = td->td_base_user_pri;
-	if (prio >= base_pri) {
-		td->td_flags &= ~TDF_UBORROWING;
-		sched_user_prio(td, base_pri);
-	} else {
-		sched_lend_user_prio(td, prio);
-	}
+	td->td_lend_user_pri = prio;
+	if (prio > base_pri)
+		td->td_user_pri = base_pri;
+	else
+		td->td_user_pri = prio;
 }
 
 void