Additional gang ABD debug code

Adding call to list_link_not_active() to avoid a logic short circuit on
the && so both prev and next are checked to see if they are pointing at
LIST_POISON values when free'ing the ABD struct. Also added check in
abd_verify() to make sure that ABD has active links when it is part of
a gang ABD.

On linux the list debug code has been setting off a failure when
checking that the node->next->prev value is pointing back at the node.
At times this check evaluates to 0xdead.

Signed-off-by: Brian Atkinson <batkinson@lanl.gov>

include/os/freebsd/spl/sys/list.h

@@ -58,6 +58,7 @@ int list_is_empty(list_t *);
 void list_link_init(list_node_t *);
 void list_link_replace(list_node_t *, list_node_t *);
 
+int list_link_not_active(list_node_t *);
 int list_link_active(list_node_t *);
 
 #ifdef	__cplusplus

include/os/linux/spl/sys/list.h

@@ -181,6 +181,12 @@ list_prev(list_t *list, void *object)
 	return (NULL);
 }
 
+static inline int
+list_link_not_active(list_node_t *node)
+{
+	return ((node->next == LIST_POISON1) && (node->prev == LIST_POISON2));
+}
+
 static inline int
 list_link_active(list_node_t *node)
 {

lib/libspl/include/sys/list.h

@@ -56,6 +56,7 @@ int list_is_empty(list_t *);
 void list_link_init(list_node_t *);
 void list_link_replace(list_node_t *, list_node_t *);
 
+int list_link_not_active(list_node_t *);
 int list_link_active(list_node_t *);
 
 #ifdef	__cplusplus

lib/libspl/list.c

@@ -229,6 +229,12 @@ list_link_init(list_node_t *ln)
 	ln->prev = NULL;
 }
 
+int
+list_link_not_active(list_node_t *in)
+{
+	return ((in->next == NULL) && (in->prev == NULL));
+}
+
 int
 list_link_active(list_node_t *ln)
 {

module/os/freebsd/spl/list.c

@@ -238,6 +238,12 @@ list_link_active(list_node_t *link)
 	return (link->list_next != NULL);
 }
 
+int
+list_link_not_active(list_node_t *link)
+{
+	return (link->list_next == NULL && link->list_prev == NULL);
+}
+
 int
 list_is_empty(list_t *list)
 {

module/os/freebsd/zfs/abd_os.c

@@ -224,7 +224,7 @@ abd_free_struct(abd_t *abd)
 	int size = MAX(sizeof (abd_t),
 	    offsetof(abd_t, abd_u.abd_scatter.abd_chunks[chunkcnt]));
 	mutex_destroy(&abd->abd_mtx);
-	ASSERT(!list_link_active(&abd->abd_gang_link));
+	ASSERT(list_link_not_active(&abd->abd_gang_link));
 	kmem_free(abd, size);
 	ABDSTAT_INCR(abdstat_struct_size, -size);
 }

module/os/linux/zfs/abd_os.c

@@ -203,7 +203,7 @@ void
 abd_free_struct(abd_t *abd)
 {
 	mutex_destroy(&abd->abd_mtx);
-	ASSERT(!list_link_active(&abd->abd_gang_link));
+	ASSERT(list_link_not_active(&abd->abd_gang_link));
 	kmem_cache_free(abd_cache, abd);
 	ABDSTAT_INCR(abdstat_struct_size, -(int)sizeof (abd_t));
 }

module/zfs/abd.c

@@ -142,6 +142,7 @@ abd_verify(abd_t *abd)
 		for (abd_t *cabd = list_head(&ABD_GANG(abd).abd_gang_chain);
 		    cabd != NULL;
 		    cabd = list_next(&ABD_GANG(abd).abd_gang_chain, cabd)) {
+			ASSERT(list_link_active(&cabd->abd_gang_link));
 			abd_verify(cabd);
 		}
 	} else {
@@ -373,6 +374,7 @@ void
 abd_gang_add(abd_t *pabd, abd_t *cabd, boolean_t free_on_free)
 {
 	ASSERT(abd_is_gang(pabd));
+	ASSERT3B(abd_is_gang(cabd), ==, B_FALSE);
 	abd_t *child_abd = NULL;
 
 	/*
@@ -422,6 +424,7 @@ abd_gang_add(abd_t *pabd, abd_t *cabd, boolean_t free_on_free)
 	ASSERT3P(child_abd, !=, NULL);
 
 	list_insert_tail(&ABD_GANG(pabd).abd_gang_chain, child_abd);
+	ASSERT3B(list_link_active(&child_abd->abd_gang_link), ==, B_TRUE);
 	mutex_exit(&cabd->abd_mtx);
 	pabd->abd_size += child_abd->abd_size;
 }