Commit c6fe44d9 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

list: add "list_del_init_careful()" to go with "list_empty_careful()" 



That gives us ordering guarantees around the pair.

Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2a9127fc

include/linux/list.h

+19 −1
Original line number Diff line number Diff line
@@ -282,6 +282,24 @@ static inline int list_empty(const struct list_head *head) 
	return READ_ONCE(head->next) == head;

}



/**

 * list_del_init_careful - deletes entry from list and reinitialize it.

 * @entry: the element to delete from the list.

 *

 * This is the same as list_del_init(), except designed to be used

 * together with list_empty_careful() in a way to guarantee ordering

 * of other memory operations.

 *

 * Any memory operations done before a list_del_init_careful() are

 * guaranteed to be visible after a list_empty_careful() test.

 */

static inline void list_del_init_careful(struct list_head *entry)

{

	__list_del_entry(entry);

	entry->prev = entry;

	smp_store_release(&entry->next, entry);

}



/**

 * list_empty_careful - tests whether a list is empty and not being modified

 * @head: the list to test
@@ -297,7 +315,7 @@ static inline int list_empty(const struct list_head *head) 
 */

static inline int list_empty_careful(const struct list_head *head)

{

	struct list_head *next = head->next;

	struct list_head *next = smp_load_acquire(&head->next);

	return (next == head) && (next == head->prev);

}

kernel/sched/wait.c

+1 −1
Original line number Diff line number Diff line
@@ -389,7 +389,7 @@ int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, i 
	int ret = default_wake_function(wq_entry, mode, sync, key);



	if (ret)

		list_del_init(&wq_entry->entry);

		list_del_init_careful(&wq_entry->entry);



	return ret;

}

mm/filemap.c

+1 −6
Original line number Diff line number Diff line
@@ -1041,13 +1041,8 @@ static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, 
	 * since after list_del_init(&wait->entry) the wait entry

	 * might be de-allocated and the process might even have

	 * exited.

	 *

	 * We _really_ should have a "list_del_init_careful()" to

	 * properly pair with the unlocked "list_empty_careful()"

	 * in finish_wait().

	 */

	smp_mb();

	list_del_init(&wait->entry);

	list_del_init_careful(&wait->entry);

	return ret;

}