io_uring: remove iopoll spinlock

commit 2dac1a1 upstream.

This reverts commit 2ccc92f

io_req_complete_post() should now behave well even in case of IOPOLL, we
can remove completion_lock locking.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7e171c8b530656b14a671c59100ca260e46e7f2a.1669203009.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

io_uring/rw.c

@@ -1043,7 +1043,6 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 	else if (!pos)
 		return 0;
 
-	spin_lock(&ctx->completion_lock);
 	prev = start;
 	wq_list_for_each_resume(pos, prev) {
 		struct io_kiocb *req = container_of(pos, struct io_kiocb, comp_list);
@@ -1058,11 +1057,11 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 		req->cqe.flags = io_put_kbuf(req, 0);
 		__io_fill_cqe_req(req->ctx, req);
 	}
-	io_commit_cqring(ctx);
-	spin_unlock(&ctx->completion_lock);
+
 	if (unlikely(!nr_events))
 		return 0;
 
+	io_commit_cqring(ctx);
 	io_cqring_ev_posted_iopoll(ctx);
 	pos = start ? start->next : ctx->iopoll_list.first;
 	wq_list_cut(&ctx->iopoll_list, prev, start);