diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c index a27ed501b6d4..15d73026ff64 100644 --- a/fs/netfs/buffered_read.c +++ b/fs/netfs/buffered_read.c @@ -168,7 +168,8 @@ void netfs_queue_read(struct netfs_io_request *rreq, * remove entries off of the front. */ spin_lock(&rreq->lock); - list_add_tail(&subreq->rreq_link, &stream->subrequests); + /* Write IN_PROGRESS before pointer to new subreq */ + list_add_tail_release(&subreq->rreq_link, &stream->subrequests); if (list_is_first(&subreq->rreq_link, &stream->subrequests)) { if (!stream->active) { stream->collected_to = subreq->start; diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c index 6df89c92b10b..21357907b7ee 100644 --- a/fs/netfs/misc.c +++ b/fs/netfs/misc.c @@ -356,6 +356,7 @@ void netfs_wait_for_in_progress_stream(struct netfs_io_request *rreq, DEFINE_WAIT(myself); list_for_each_entry(subreq, &stream->subrequests, rreq_link) { + smp_rmb(); /* Read ->next before IN_PROGRESS. */ if (!netfs_check_subreq_in_progress(subreq)) continue; diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c index d2d902f46627..3c9b847885c2 100644 --- a/fs/netfs/read_collect.c +++ b/fs/netfs/read_collect.c @@ -205,8 +205,10 @@ static void netfs_collect_read_results(struct netfs_io_request *rreq) * in progress. The issuer thread may be adding stuff to the tail * whilst we're doing this. */ - front = list_first_entry_or_null(&stream->subrequests, - struct netfs_io_subrequest, rreq_link); + front = list_first_entry_or_null_acquire(&stream->subrequests, + struct netfs_io_subrequest, rreq_link); + /* Read first subreq pointer before IN_PROGRESS flag. */ + while (front) { size_t transferred; diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c index b194447f4b11..7fbf50907a7f 100644 --- a/fs/netfs/write_collect.c +++ b/fs/netfs/write_collect.c @@ -228,8 +228,10 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq) if (!smp_load_acquire(&stream->active)) continue; - front = list_first_entry_or_null(&stream->subrequests, - struct netfs_io_subrequest, rreq_link); + front = list_first_entry_or_null_acquire(&stream->subrequests, + struct netfs_io_subrequest, rreq_link); + /* Read first subreq pointer before IN_PROGRESS flag. */ + while (front) { trace_netfs_collect_sreq(wreq, front); //_debug("sreq [%x] %llx %zx/%zx", diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c index 2db688f94125..b0e9690bb90c 100644 --- a/fs/netfs/write_issue.c +++ b/fs/netfs/write_issue.c @@ -204,7 +204,8 @@ void netfs_prepare_write(struct netfs_io_request *wreq, * remove entries off of the front. */ spin_lock(&wreq->lock); - list_add_tail(&subreq->rreq_link, &stream->subrequests); + /* Write IN_PROGRESS before pointer to new subreq */ + list_add_tail_release(&subreq->rreq_link, &stream->subrequests); if (list_is_first(&subreq->rreq_link, &stream->subrequests)) { if (!stream->active) { stream->collected_to = subreq->start; diff --git a/include/linux/list.h b/include/linux/list.h index 00ea8e5fb88b..09d979976b3b 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -191,6 +191,29 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head) __list_add(new, head->prev, head); } +/** + * list_add_tail_release - add a new entry with release barrier + * @new: new entry to be added + * @head: list head to add it before + * + * Insert a new entry before the specified head, using a release barrier to set + * the ->next pointer that points to it. This is useful for implementing + * queues, in particular one that the elements will be walked through forwards + * locklessly. + */ +static inline void list_add_tail_release(struct list_head *new, + struct list_head *head) +{ + struct list_head *prev = head->prev; + + if (__list_add_valid(new, prev, head)) { + new->next = head; + new->prev = prev; + head->prev = new; + smp_store_release(&prev->next, new); + } +} + /* * Delete a list entry by making the prev/next entries * point to each other. @@ -644,6 +667,20 @@ static inline void list_splice_tail_init(struct list_head *list, pos__ != head__ ? list_entry(pos__, type, member) : NULL; \ }) +/** + * list_first_entry_or_null_acquire - get the first element from a list with barrier + * @ptr: the list head to take the element from. + * @type: the type of the struct this is embedded in. + * @member: the name of the list_head within the struct. + * + * Note that if the list is empty, it returns NULL. + */ +#define list_first_entry_or_null_acquire(ptr, type, member) ({ \ + struct list_head *head__ = (ptr); \ + struct list_head *pos__ = smp_load_acquire(&head__->next); \ + pos__ != head__ ? list_entry(pos__, type, member) : NULL; \ +}) + /** * list_last_entry_or_null - get the last element from a list * @ptr: the list head to take the element from.