[S390] qdio: prevent handling of buffers if count is zero

Exit do_QDIO early if the buffer count is zero to prevent side effects
in the following functions.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c
index 5640c89cd9d..479c665e9e7 100644
--- a/drivers/s390/cio/qdio_main.c
+++ b/drivers/s390/cio/qdio_main.c
@@ -1508,7 +1508,8 @@ int do_QDIO(struct ccw_device *cdev, unsigned int callflags,
 
         if (irq_ptr->state != QDIO_IRQ_STATE_ACTIVE)
                 return -EBUSY;
-
+        if (!count)
+                return 0;
         if (callflags & QDIO_FLAG_SYNC_INPUT)
                 return handle_inbound(irq_ptr->input_qs[q_nr],
                                       callflags, bufnr, count);