Add sanity checking for QUEUE(3) TAILQs under INVARIANTS (similar to

the LIST checks).  Races may lead to list corruption, which can be
difficult to unravel in a post-mortem analysis.  These checks verify
that the prev and next pointers are consistent when inserting or
removing elements, thus catching any corruption earlier.

1 files changed, 37 insertions, 0 deletions

diff --git a/sys/sys/queue.h b/sys/sys/queue.h
index 3bf12d2..74b8d86 100644
--- a/sys/sys/queue.h
+++ b/sys/sys/queue.h
@@ -430,6 +430,37 @@ struct {								\
 /*
  * Tail queue functions.
  */
+#if (defined(_KERNEL) && defined(INVARIANTS))
+#define	QMD_TAILQ_CHECK_HEAD(head, field) do {				\
+	if (!TAILQ_EMPTY(head) &&					\
+	    TAILQ_FIRST((head))->field.tqe_prev !=			\
+	     &TAILQ_FIRST((head)))					\
+		panic("Bad tailq head %p first->prev != head", (head));	\
+} while (0)
+
+#define	QMD_TAILQ_CHECK_TAIL(head, field) do {				\
+	if (*(head)->tqh_last != NULL)					\
+	    	panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head)); 	\
+} while (0)
+
+#define	QMD_TAILQ_CHECK_NEXT(elm, field) do {				\
+	if (TAILQ_NEXT((elm), field) != NULL &&				\
+	    TAILQ_NEXT((elm), field)->field.tqe_prev !=			\
+	     &((elm)->field.tqe_next))					\
+		panic("Bad link elm %p next->prev != elm", (elm));	\
+} while (0)
+
+#define	QMD_TAILQ_CHECK_PREV(elm, field) do {				\
+	if (*(elm)->field.tqe_prev != (elm))				\
+		panic("Bad link elm %p prev->next != elm", (elm));	\
+} while (0)
+#else
+#define	QMD_TAILQ_CHECK_HEAD(head, field)
+#define	QMD_TAILQ_CHECK_TAIL(head, headname)
+#define	QMD_TAILQ_CHECK_NEXT(elm, field)
+#define	QMD_TAILQ_CHECK_PREV(elm, field)
+#endif /* (_KERNEL && INVARIANTS) */
+
 #define	TAILQ_CONCAT(head1, head2, field) do {				\
 	if (!TAILQ_EMPTY(head2)) {					\
 		*(head1)->tqh_last = (head2)->tqh_first;		\
@@ -472,6 +503,7 @@ struct {								\
 } while (0)
 
 #define	TAILQ_INSERT_AFTER(head, listelm, elm, field) do {		\
+	QMD_TAILQ_CHECK_NEXT(listelm, field);				\
 	if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 		TAILQ_NEXT((elm), field)->field.tqe_prev = 		\
 		    &TAILQ_NEXT((elm), field);				\
@@ -486,6 +518,7 @@ struct {								\
 } while (0)
 
 #define	TAILQ_INSERT_BEFORE(listelm, elm, field) do {			\
+	QMD_TAILQ_CHECK_PREV(listelm, field);				\
 	(elm)->field.tqe_prev = (listelm)->field.tqe_prev;		\
 	TAILQ_NEXT((elm), field) = (listelm);				\
 	*(listelm)->field.tqe_prev = (elm);				\
@@ -495,6 +528,7 @@ struct {								\
 } while (0)
 
 #define	TAILQ_INSERT_HEAD(head, elm, field) do {			\
+	QMD_TAILQ_CHECK_HEAD(head, field);				\
 	if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)	\
 		TAILQ_FIRST((head))->field.tqe_prev =			\
 		    &TAILQ_NEXT((elm), field);				\
@@ -507,6 +541,7 @@ struct {								\
 } while (0)
 
 #define	TAILQ_INSERT_TAIL(head, elm, field) do {			\
+	QMD_TAILQ_CHECK_TAIL(head, field);				\
 	TAILQ_NEXT((elm), field) = NULL;				\
 	(elm)->field.tqe_prev = (head)->tqh_last;			\
 	*(head)->tqh_last = (elm);					\
@@ -524,6 +559,8 @@ struct {								\
 	(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 
 #define	TAILQ_REMOVE(head, elm, field) do {				\
+	QMD_TAILQ_CHECK_NEXT(elm, field);				\
+	QMD_TAILQ_CHECK_PREV(elm, field);				\
 	if ((TAILQ_NEXT((elm), field)) != NULL)				\
 		TAILQ_NEXT((elm), field)->field.tqe_prev = 		\
 		    (elm)->field.tqe_prev;				\