2 files changed, 22 insertions, 0 deletions

diff --git a/sys/kern/subr_witness.c b/sys/kern/subr_witness.c
index c0d111f7aa46..10891be2fcf5 100644
--- a/sys/kern/subr_witness.c
+++ b/sys/kern/subr_witness.c
@@ -1593,6 +1593,27 @@ witness_list_locks(struct lock_list_entry **lock_list)
 	return (nheld);
 }
 
+/*
+ * This is a bit risky at best.  We call this function when we have timed
+ * out acquiring a spin lock, and we assume that the other CPU is stuck
+ * with this lock held.  So, we go groveling around in the other CPU's
+ * per-cpu data to try to find the lock instance for this spin lock to
+ * see when it was last acquired.
+ */
+void
+witness_display_spinlock(struct lock_object *lock, struct thread *owner)
+{
+	struct lock_instance *instance;
+	struct pcpu *pc;
+
+	if (owner->td_critnest == 0 || owner->td_oncpu == NOCPU)
+		return;
+	pc = pcpu_find(owner->td_oncpu);
+	instance = find_instance(pc->pc_spinlocks, lock);
+	if (instance != NULL)
+		witness_list_lock(instance);
+}
+
 void
 witness_save(struct lock_object *lock, const char **filep, int *linep)
 {
diff --git a/sys/sys/lock.h b/sys/sys/lock.h
index 106018bfb333..dcf7b772217a 100644
--- a/sys/sys/lock.h
+++ b/sys/sys/lock.h
@@ -206,6 +206,7 @@ void	witness_restore(struct lock_object *, const char *, int);
 int	witness_list_locks(struct lock_list_entry **);
 int	witness_warn(int, struct lock_object *, const char *, ...);
 void	witness_assert(struct lock_object *, int, const char *, int);
+void	witness_display_spinlock(struct lock_object *, struct thread *);
 int	witness_line(struct lock_object *);
 const char *witness_file(struct lock_object *);