[S390] tape: deadlock on system work queue

The 34xx and 3590 tape driver uses the system work queue to defer work
from the interrupt function to process context, e.g. a medium sense
after an unsolicited interrupt. The tape commands started by the work
handler need to be asynchronous, otherwise a deadlock on the system
work queue can occur.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 41 insertions, 18 deletions

diff --git a/drivers/s390/char/tape_34xx.c b/drivers/s390/char/tape_34xx.c
index c17f35b6136a..c26511171ffe 100644
--- a/drivers/s390/char/tape_34xx.c
+++ b/drivers/s390/char/tape_34xx.c
@@ -53,23 +53,11 @@ static void tape_34xx_delete_sbid_from(struct tape_device *, int);
  * Medium sense for 34xx tapes. There is no 'real' medium sense call.
  * So we just do a normal sense.
  */
-static int
-tape_34xx_medium_sense(struct tape_device *device)
+static void __tape_34xx_medium_sense(struct tape_request *request)
 {
-	struct tape_request *request;
-	unsigned char       *sense;
-	int                  rc;
-
-	request = tape_alloc_request(1, 32);
-	if (IS_ERR(request)) {
-		DBF_EXCEPTION(6, "MSEN fail\n");
-		return PTR_ERR(request);
-	}
-
-	request->op = TO_MSEN;
-	tape_ccw_end(request->cpaddr, SENSE, 32, request->cpdata);
+	struct tape_device *device = request->device;
+	unsigned char *sense;
 
-	rc = tape_do_io_interruptible(device, request);
 	if (request->rc == 0) {
 		sense = request->cpdata;
 
@@ -88,15 +76,47 @@ tape_34xx_medium_sense(struct tape_device *device)
 			device->tape_generic_status |= GMT_WR_PROT(~0);
 		else
 			device->tape_generic_status &= ~GMT_WR_PROT(~0);
-	} else {
+	} else
 		DBF_EVENT(4, "tape_34xx: medium sense failed with rc=%d\n",
 			request->rc);
-	}
 	tape_free_request(request);
+}
+
+static int tape_34xx_medium_sense(struct tape_device *device)
+{
+	struct tape_request *request;
+	int rc;
+
+	request = tape_alloc_request(1, 32);
+	if (IS_ERR(request)) {
+		DBF_EXCEPTION(6, "MSEN fail\n");
+		return PTR_ERR(request);
+	}
 
+	request->op = TO_MSEN;
+	tape_ccw_end(request->cpaddr, SENSE, 32, request->cpdata);
+	rc = tape_do_io_interruptible(device, request);
+	__tape_34xx_medium_sense(request);
 	return rc;
 }
 
+static void tape_34xx_medium_sense_async(struct tape_device *device)
+{
+	struct tape_request *request;
+
+	request = tape_alloc_request(1, 32);
+	if (IS_ERR(request)) {
+		DBF_EXCEPTION(6, "MSEN fail\n");
+		return;
+	}
+
+	request->op = TO_MSEN;
+	tape_ccw_end(request->cpaddr, SENSE, 32, request->cpdata);
+	request->callback = (void *) __tape_34xx_medium_sense;
+	request->callback_data = NULL;
+	tape_do_io_async(device, request);
+}
+
 struct tape_34xx_work {
 	struct tape_device	*device;
 	enum tape_op		 op;
@@ -109,6 +129,9 @@ struct tape_34xx_work {
  * is inserted but cannot call tape_do_io* from an interrupt context.
  * Maybe that's useful for other actions we want to start from the
  * interrupt handler.
+ * Note: the work handler is called by the system work queue. The tape
+ * commands started by the handler need to be asynchrounous, otherwise
+ * a deadlock can occur e.g. in case of a deferred cc=1 (see __tape_do_irq).
  */
 static void
 tape_34xx_work_handler(struct work_struct *work)
@@ -119,7 +142,7 @@ tape_34xx_work_handler(struct work_struct *work)
 
 	switch(p->op) {
 		case TO_MSEN:
-			tape_34xx_medium_sense(device);
+			tape_34xx_medium_sense_async(device);
 			break;
 		default:
 			DBF_EVENT(3, "T34XX: internal error: unknown work\n");