io_uring: hook all linked requests via link_list

Links are created by chaining requests through req->list with an
exception that head uses req->link_list. (e.g. link_list->list->list)
Because of that, io_req_link_next() needs complex splicing to advance.

Link them all through list_list. Also, it seems to be simpler and more
consistent IMHO.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1fca9e2..c838705 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -916,7 +916,6 @@ static bool io_link_cancel_timeout(struct io_kiocb *req)
 static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
 {
        struct io_ring_ctx *ctx = req->ctx;
-       struct io_kiocb *nxt;
        bool wake_ev = false;
 
        /* Already got next link */
@@ -928,24 +927,21 @@ static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
         * potentially happen if the chain is messed up, check to be on the
         * safe side.
         */
-       nxt = list_first_entry_or_null(&req->link_list, struct io_kiocb, list);
-       while (nxt) {
-               list_del_init(&nxt->list);
+       while (!list_empty(&req->link_list)) {
+               struct io_kiocb *nxt = list_first_entry(&req->link_list,
+                                               struct io_kiocb, link_list);
 
-               if ((req->flags & REQ_F_LINK_TIMEOUT) &&
-                   (nxt->flags & REQ_F_TIMEOUT)) {
+               if (unlikely((req->flags & REQ_F_LINK_TIMEOUT) &&
+                            (nxt->flags & REQ_F_TIMEOUT))) {
+                       list_del_init(&nxt->link_list);
                        wake_ev |= io_link_cancel_timeout(nxt);
-                       nxt = list_first_entry_or_null(&req->link_list,
-                                                       struct io_kiocb, list);
                        req->flags &= ~REQ_F_LINK_TIMEOUT;
                        continue;
                }
-               if (!list_empty(&req->link_list)) {
-                       INIT_LIST_HEAD(&nxt->link_list);
-                       list_splice(&req->link_list, &nxt->link_list);
-                       nxt->flags |= REQ_F_LINK;
-               }
 
+               list_del_init(&req->link_list);
+               if (!list_empty(&nxt->link_list))
+                       nxt->flags |= REQ_F_LINK;
                *nxtptr = nxt;
                break;
        }
@@ -961,15 +957,15 @@ static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
 static void io_fail_links(struct io_kiocb *req)
 {
        struct io_ring_ctx *ctx = req->ctx;
-       struct io_kiocb *link;
        unsigned long flags;
 
        spin_lock_irqsave(&ctx->completion_lock, flags);
 
        while (!list_empty(&req->link_list)) {
-               link = list_first_entry(&req->link_list, struct io_kiocb, list);
-               list_del_init(&link->list);
+               struct io_kiocb *link = list_first_entry(&req->link_list,
+                                               struct io_kiocb, link_list);
 
+               list_del_init(&link->link_list);
                trace_io_uring_fail_link(req, link);
 
                if ((req->flags & REQ_F_LINK_TIMEOUT) &&
@@ -3170,10 +3166,11 @@ static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
         * 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->list)) {
-               prev = list_entry(req->list.prev, struct io_kiocb, link_list);
+       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->list);
+                       list_del_init(&req->link_list);
                        prev->flags &= ~REQ_F_LINK_TIMEOUT;
                } else
                        prev = NULL;
@@ -3203,7 +3200,7 @@ static void io_queue_linked_timeout(struct io_kiocb *req)
         * we got a chance to setup the timer
         */
        spin_lock_irq(&ctx->completion_lock);
-       if (!list_empty(&req->list)) {
+       if (!list_empty(&req->link_list)) {
                struct io_timeout_data *data = &req->io->timeout;
 
                data->timer.function = io_link_timeout_fn;
@@ -3223,7 +3220,8 @@ static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req)
        if (!(req->flags & REQ_F_LINK))
                return NULL;
 
-       nxt = list_first_entry_or_null(&req->link_list, struct io_kiocb, list);
+       nxt = list_first_entry_or_null(&req->link_list, struct io_kiocb,
+                                       link_list);
        if (!nxt || nxt->sqe->opcode != IORING_OP_LINK_TIMEOUT)
                return NULL;
 
@@ -3364,7 +3362,7 @@ err_req:
                        goto err_req;
                }
                trace_io_uring_link(ctx, req, prev);
-               list_add_tail(&req->list, &prev->link_list);
+               list_add_tail(&req->link_list, &prev->link_list);
        } else if (req->sqe->flags & IOSQE_IO_LINK) {
                req->flags |= REQ_F_LINK;