io_uring: split iopoll loop

The main loop of io_do_iopoll() iterates and does ->iopoll() until it
meets a first completed request, then it continues from that position
and splices requests to pass them through io_iopoll_complete().

Split the loop in two for clearness, iopolling and reaping completed
requests from the list.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a7f6fd27a94845e5dc925a47a4a9765a92e514fb.1632516769.git.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 90ad9cd..0e46ed6 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2441,6 +2441,12 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, struct list_head *done)
        io_req_free_batch_finish(ctx, &rb);
 }
 
+/* same as "continue" but starts from the pos, not next to it */
+#define list_for_each_entry_safe_resume(pos, n, head, member)          \
+       for (n = list_next_entry(pos, member);                          \
+            !list_entry_is_head(pos, head, member);                    \
+            pos = n, n = list_next_entry(n, member))
+
 static int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 {
        struct io_kiocb *req, *tmp;
@@ -2456,7 +2462,7 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
        if (ctx->poll_multi_queue || force_nonspin)
                poll_flags |= BLK_POLL_ONESHOT;
 
-       list_for_each_entry_safe(req, tmp, &ctx->iopoll_list, inflight_entry) {
+       list_for_each_entry(req, &ctx->iopoll_list, inflight_entry) {
                struct kiocb *kiocb = &req->rw.kiocb;
                int ret;
 
@@ -2465,12 +2471,7 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
                 * If we find a request that requires polling, break out
                 * and complete those lists first, if we have entries there.
                 */
-               if (READ_ONCE(req->iopoll_completed)) {
-                       list_move_tail(&req->inflight_entry, &done);
-                       nr_events++;
-                       continue;
-               }
-               if (!list_empty(&done))
+               if (READ_ONCE(req->iopoll_completed))
                        break;
 
                ret = kiocb->ki_filp->f_op->iopoll(kiocb, &iob, poll_flags);
@@ -2481,17 +2482,22 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 
                /* iopoll may have completed current req */
                if (!rq_list_empty(iob.req_list) ||
-                   READ_ONCE(req->iopoll_completed)) {
-                       list_move_tail(&req->inflight_entry, &done);
-                       nr_events++;
-               }
+                   READ_ONCE(req->iopoll_completed))
+                       break;
        }
 
        if (!rq_list_empty(iob.req_list))
                iob.complete(&iob);
-       if (!list_empty(&done))
-               io_iopoll_complete(ctx, &done);
+       list_for_each_entry_safe_resume(req, tmp, &ctx->iopoll_list,
+                                       inflight_entry) {
+               if (!READ_ONCE(req->iopoll_completed))
+                       break;
+               list_move_tail(&req->inflight_entry, &done);
+               nr_events++;
+       }
 
+       if (nr_events)
+               io_iopoll_complete(ctx, &done);
        return nr_events;
 }