firewire: ohci: use workqueue to handle events of AT request/response contexts

This commit adds a work item to handle events of 1394 OHCI AT
request/response contexts, and queues the item to the specific
workqueue. The call of struct fw_packet.callbaqck() is done in the
workqueue when receiving acknowledgement to the asynchronous packet
transferred to remote node.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Takashi Sakamoto <[e-mail]>

drivers/firewire/net.c

···
 
 		spin_lock_irqsave(&dev->lock, flags);
 
-		/* If the AT tasklet already ran, we may be last user. */
+		/* If the AT work item already ran, we may be last user. */
 		free = (ptask->outstanding_pkts == 0 && !ptask->enqueued);
 		if (!free)
 			ptask->enqueued = true;
···
 
 	spin_lock_irqsave(&dev->lock, flags);
 
-	/* If the AT tasklet already ran, we may be last user. */
+	/* If the AT work item already ran, we may be last user. */
 	free = (ptask->outstanding_pkts == 0 && !ptask->enqueued);
 	if (!free)
 		ptask->enqueued = true;

drivers/firewire/ohci.c

···
 
 	descriptor_callback_t callback;
 
-	struct tasklet_struct tasklet;
+	struct work_struct work;
 };
 
 struct iso_context {
···
 	}
 }
 
-static void context_tasklet(unsigned long data)
+static void ohci_at_context_work(struct work_struct *work)
 {
-	struct context *ctx = (struct context *) data;
+	struct context *ctx = from_work(ctx, work, work);
 
 	context_retire_descriptors(ctx);
 }
···
 	ctx->buffer_tail = list_entry(ctx->buffer_list.next,
 			struct descriptor_buffer, list);
 
-	tasklet_init(&ctx->tasklet, context_tasklet, (unsigned long)ctx);
 	ctx->callback = callback;
 
 	/*
···
 
 static void at_context_flush(struct context *ctx)
 {
-	tasklet_disable(&ctx->tasklet);
+	// Avoid dead lock due to programming mistake.
+	if (WARN_ON_ONCE(current_work() == &ctx->work))
+		return;
 
-	ctx->flushing = true;
-	context_tasklet((unsigned long)ctx);
-	ctx->flushing = false;
+	disable_work_sync(&ctx->work);
 
-	tasklet_enable(&ctx->tasklet);
+	WRITE_ONCE(ctx->flushing, true);
+	ohci_at_context_work(&ctx->work);
+	WRITE_ONCE(ctx->flushing, false);
+
+	enable_work(&ctx->work);
 }
 
 static int handle_at_packet(struct context *context,
···
 	struct fw_ohci *ohci = context->ohci;
 	int evt;
 
-	if (last->transfer_status == 0 && !context->flushing)
+	if (last->transfer_status == 0 && !READ_ONCE(context->flushing))
 		/* This descriptor isn't done yet, stop iteration. */
 		return 0;
 
···
 		break;
 
 	case OHCI1394_evt_missing_ack:
-		if (context->flushing)
+		if (READ_ONCE(context->flushing))
 			packet->ack = RCODE_GENERATION;
 		else {
 			/*
···
 		break;
 
 	case OHCI1394_evt_no_status:
-		if (context->flushing) {
+		if (READ_ONCE(context->flushing)) {
 			packet->ack = RCODE_GENERATION;
 			break;
 		}
···
 		queue_work(ohci->card.async_wq, &ohci->ar_response_ctx.work);
 
 	if (event & OHCI1394_reqTxComplete)
-		tasklet_schedule(&ohci->at_request_ctx.tasklet);
+		queue_work(ohci->card.async_wq, &ohci->at_request_ctx.work);
 
 	if (event & OHCI1394_respTxComplete)
-		tasklet_schedule(&ohci->at_response_ctx.tasklet);
+		queue_work(ohci->card.async_wq, &ohci->at_response_ctx.work);
 
 	if (event & OHCI1394_isochRx) {
 		iso_event = reg_read(ohci, OHCI1394_IsoRecvIntEventClear);
···
 	struct driver_data *driver_data = packet->driver_data;
 	int ret = -ENOENT;
 
-	tasklet_disable_in_atomic(&ctx->tasklet);
+	// Avoid dead lock due to programming mistake.
+	if (WARN_ON_ONCE(current_work() == &ctx->work))
+		return 0;
+	disable_work_sync(&ctx->work);
 
 	if (packet->ack != 0)
 		goto out;
···
 	packet->callback(packet, &ohci->card, packet->ack);
 	ret = 0;
  out:
-	tasklet_enable(&ctx->tasklet);
+	enable_work(&ctx->work);
 
 	return ret;
 }
···
 			   OHCI1394_AsReqTrContextControlSet, handle_at_packet);
 	if (err < 0)
 		return err;
+	INIT_WORK(&ohci->at_request_ctx.work, ohci_at_context_work);
 
 	err = context_init(&ohci->at_response_ctx, ohci,
 			   OHCI1394_AsRspTrContextControlSet, handle_at_packet);
 	if (err < 0)
 		return err;
+	INIT_WORK(&ohci->at_response_ctx.work, ohci_at_context_work);
 
 	reg_write(ohci, OHCI1394_IsoRecvIntMaskSet, ~0);
 	ohci->ir_context_channels = ~0ULL;

include/linux/firewire.h

···
 	 * For successful transmission, the status code is the ack received
 	 * from the destination.  Otherwise it is one of the juju-specific
 	 * rcodes:  RCODE_SEND_ERROR, _CANCELLED, _BUSY, _GENERATION, _NO_ACK.
-	 * The callback can be called from tasklet context and thus
-	 * must never block.
+	 * The callback can be called from workqueue and thus must never block.
 	 */
 	fw_packet_callback_t callback;
 	int ack;
···
  *
  * A variation of __fw_send_request() to generate callback for response subaction without time
  * stamp.
+ *
+ * The callback is invoked in the workqueue context in most cases. However, if an error is detected
+ * before queueing or the destination address refers to the local node, it is invoked in the
+ * current context instead.
  */
 static inline void fw_send_request(struct fw_card *card, struct fw_transaction *t, int tcode,
 				   int destination_id, int generation, int speed,
···
  * @callback_data:	data to be passed to the transaction completion callback
  *
  * A variation of __fw_send_request() to generate callback for response subaction with time stamp.
+ *
+ * The callback is invoked in the workqueue context in most cases. However, if an error is detected
+ * before queueing or the destination address refers to the local node, it is invoked in the current
+ * context instead.
  */
 static inline void fw_send_request_with_tstamp(struct fw_card *card, struct fw_transaction *t,
 	int tcode, int destination_id, int generation, int speed, unsigned long long offset,