[PATCH 2/4] io_uring: track link timeout's master explicitly

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

In preparation for converting singly linked lists for chaining requests,
make linked timeouts save requests that they're responsible for and not
count on doubly linked list for back referencing.

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 fs/io_uring.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index ce092d6cab73..4eb1cb8a8bf8 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -445,6 +445,8 @@ struct io_timeout {
 	u32				off;
 	u32				target_seq;
 	struct list_head		list;
+	/* head of the link, used by linked timeouts only */
+	struct io_kiocb			*head;
 };
 
 struct io_timeout_rem {
@@ -1871,6 +1873,7 @@ static void io_kill_linked_timeout(struct io_kiocb *req)
 		int ret;
 
 		list_del_init(&link->link_list);
+		link->timeout.head = NULL;
 		ret = hrtimer_try_to_cancel(&io->timer);
 		if (ret != -1) {
 			io_cqring_fill_event(link, -ECANCELED);
@@ -6084,26 +6087,22 @@ static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
 {
 	struct io_timeout_data *data = container_of(timer,
 						struct io_timeout_data, timer);
-	struct io_kiocb *req = data->req;
+	struct io_kiocb *prev, *req = data->req;
 	struct io_ring_ctx *ctx = req->ctx;
-	struct io_kiocb *prev = NULL;
 	unsigned long flags;
 
 	spin_lock_irqsave(&ctx->completion_lock, flags);
+	prev = req->timeout.head;
+	req->timeout.head = NULL;
 
 	/*
 	 * We don't expect the list to be empty, that will only happen if we
 	 * race with the completion of the linked work.
 	 */
-	if (!list_empty(&req->link_list)) {
-		prev = list_entry(req->link_list.prev, struct io_kiocb,
-				  link_list);
-		if (refcount_inc_not_zero(&prev->refs))
-			list_del_init(&req->link_list);
-		else
-			prev = NULL;
-	}
-
+	if (prev && refcount_inc_not_zero(&prev->refs))
+		list_del_init(&req->link_list);
+	else
+		prev = NULL;
 	spin_unlock_irqrestore(&ctx->completion_lock, flags);
 
 	if (prev) {
@@ -6122,7 +6121,7 @@ static void __io_queue_linked_timeout(struct io_kiocb *req)
 	 * If the list is now empty, then our linked request finished before
 	 * we got a chance to setup the timer
 	 */
-	if (!list_empty(&req->link_list)) {
+	if (req->timeout.head) {
 		struct io_timeout_data *data = req->async_data;
 
 		data->timer.function = io_link_timeout_fn;
@@ -6157,6 +6156,7 @@ static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req)
 	if (!nxt || nxt->opcode != IORING_OP_LINK_TIMEOUT)
 		return NULL;
 
+	nxt->timeout.head = req;
 	nxt->flags |= REQ_F_LTIMEOUT_ACTIVE;
 	req->flags |= REQ_F_LINK_TIMEOUT;
 	return nxt;
-- 
2.24.0