Commit 1658d35e authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 1c97be67

include/linux/list.h

+2 −2
Original line number Diff line number Diff line
@@ -186,7 +186,7 @@ static inline int list_is_last(const struct list_head *list, 
 */

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_unhashed(const struct hlist_node *h) 


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)

include/linux/list_bl.h

+1 −1
Original line number Diff line number Diff line
@@ -70,7 +70,7 @@ static inline void hlist_bl_set_first(struct hlist_bl_head *h, 


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,

include/linux/list_nulls.h

+1 −1
Original line number Diff line number Diff line
@@ -57,7 +57,7 @@ static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h) 


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,

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