io_uring: recycle provided buffers if request goes async

If we are using provided buffers, it's less than useful to have a buffer
selected and pinned if a request needs to go async or arms poll for
notification trigger on when we can process it.

Recycle the buffer in those events, so we don't pin it for the duration
of the request.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -269,6 +269,7 @@ struct io_buffer {
 	__u64 addr;
 	__u32 len;
 	__u16 bid;
+	__u16 bgid;
 };
 
 struct io_restriction {
@@ -1351,6 +1352,36 @@ static inline unsigned int io_put_kbuf(struct io_kiocb *req,
 	return cflags;
 }
 
+static void io_kbuf_recycle(struct io_kiocb *req)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_buffer *head, *buf;
+
+	if (likely(!(req->flags & REQ_F_BUFFER_SELECTED)))
+		return;
+
+	lockdep_assert_held(&ctx->uring_lock);
+
+	buf = req->kbuf;
+
+	head = xa_load(&ctx->io_buffers, buf->bgid);
+	if (head) {
+		list_add(&buf->list, &head->list);
+	} else {
+		int ret;
+
+		INIT_LIST_HEAD(&buf->list);
+
+		/* if we fail, just leave buffer attached */
+		ret = xa_insert(&ctx->io_buffers, buf->bgid, buf, GFP_KERNEL);
+		if (unlikely(ret < 0))
+			return;
+	}
+
+	req->flags &= ~REQ_F_BUFFER_SELECTED;
+	req->kbuf = NULL;
+}
+
 static bool io_match_task(struct io_kiocb *head, struct task_struct *task,
 			  bool cancel_all)
 	__must_hold(&req->ctx->timeout_lock)
@@ -4763,6 +4794,7 @@ static int io_add_buffers(struct io_ring_ctx *ctx, struct io_provide_buf *pbuf,
 		buf->addr = addr;
 		buf->len = min_t(__u32, pbuf->len, MAX_RW_COUNT);
 		buf->bid = bid;
+		buf->bgid = pbuf->bgid;
 		addr += pbuf->len;
 		bid++;
 		if (!*head) {
@@ -7395,8 +7427,12 @@ static void io_queue_sqe_arm_apoll(struct io_kiocb *req)
 		 * Queued up for async execution, worker will release
 		 * submit reference when the iocb is actually submitted.
 		 */
+		io_kbuf_recycle(req);
 		io_queue_async_work(req, NULL);
 		break;
+	case IO_APOLL_OK:
+		io_kbuf_recycle(req);
+		break;
 	}
 
 	if (linked_timeout)