From: Linus Torvalds torvalds@linux-foundation.org
[ Upstream commit c6fe44d96fc1536af5b11cd859686453d1b7bfd1 ]
That gives us ordering guarantees around the pair.
Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Stable-dep-of: 2192bba03d80 ("epoll: ep_autoremove_wake_function should use list_del_init_careful") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/list.h | 20 +++++++++++++++++++- kernel/sched/wait.c | 2 +- mm/filemap.c | 7 +------ 3 files changed, 21 insertions(+), 8 deletions(-)
diff --git a/include/linux/list.h b/include/linux/list.h index ce19c6b632a59..231ff089f7d1c 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -268,6 +268,24 @@ 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 @@ -283,7 +301,7 @@ 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); }
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c index 7d668b31dbc6d..c76fe1d4d91e2 100644 --- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -384,7 +384,7 @@ 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; } diff --git a/mm/filemap.c b/mm/filemap.c index 83b324420046b..a106d63e84679 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1085,13 +1085,8 @@ 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; }