list: Use READ_ONCE() when testing for empty lists
Most of the list-empty-check macros (list_empty(), hlist_empty(),
hlist_bl_empty(), hlist_nulls_empty(), and hlist_nulls_empty()) use
an unadorned load to check the list header. Given that these macros
are sometimes invoked without the protection of a lock, this is
not sufficient. This commit therefore adds READ_ONCE() calls to
them. This commit does not touch llist_empty() because it already
has the needed ACCESS_ONCE().
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/list.h b/include/linux/list.h
index d7e31fe..06c2d88 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -186,7 +186,7 @@
*/
static inline int list_empty(const struct list_head *head)
{
- return head->next == head;
+ return READ_ONCE(head->next) == head;
}
/**
@@ -608,7 +608,7 @@
static inline int hlist_empty(const struct hlist_head *h)
{
- return !h->first;
+ return !READ_ONCE(h->first);
}
static inline void __hlist_del(struct hlist_node *n)
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index 8132214..ee7229a 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -70,7 +70,7 @@
static inline int hlist_bl_empty(const struct hlist_bl_head *h)
{
- return !((unsigned long)h->first & ~LIST_BL_LOCKMASK);
+ return !((unsigned long)READ_ONCE(h->first) & ~LIST_BL_LOCKMASK);
}
static inline void hlist_bl_add_head(struct hlist_bl_node *n,
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index 444d2b1..b01fe10 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -57,7 +57,7 @@
static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
{
- return is_a_nulls(h->first);
+ return is_a_nulls(READ_ONCE(h->first));
}
static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,