[S390] tape: fix race with stack local wait_queue_head_t.

A wait_event call with a stack local wait_queue_head_t structure that is
used to do the wake up for the wait_event is inherently racy. After the
wait_event finished the wake_up call might not have completed yet.
Replace the stack local wait_queue_head_t in tape_do_io and
tape_do_io_interruptible with a per device wait queue.

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

2 files changed, 10 insertions, 9 deletions

diff --git a/drivers/s390/char/tape.h b/drivers/s390/char/tape.h
index dddf8d62c153..d0d565a05dfe 100644
--- a/drivers/s390/char/tape.h
+++ b/drivers/s390/char/tape.h
@@ -231,6 +231,9 @@ struct tape_device {
         /* Request queue. */
         struct list_head                req_queue;
 
+        /* Request wait queue. */
+        wait_queue_head_t               wait_queue;
+
         /* Each tape device has (currently) two minor numbers. */
         int                             first_minor;
 
diff --git a/drivers/s390/char/tape_core.c b/drivers/s390/char/tape_core.c
index 76e44eb7c47f..c20e3c548343 100644
--- a/drivers/s390/char/tape_core.c
+++ b/drivers/s390/char/tape_core.c
@@ -449,6 +449,7 @@ tape_alloc_device(void)
         INIT_LIST_HEAD(&device->req_queue);
         INIT_LIST_HEAD(&device->node);
         init_waitqueue_head(&device->state_change_wq);
+        init_waitqueue_head(&device->wait_queue);
         device->tape_state = TS_INIT;
         device->medium_state = MS_UNKNOWN;
         *device->modeset_byte = 0;
@@ -954,21 +955,19 @@ __tape_wake_up(struct tape_request *request, void *data)
 int
 tape_do_io(struct tape_device *device, struct tape_request *request)
 {
-        wait_queue_head_t wq;
         int rc;
 
-        init_waitqueue_head(&wq);
         spin_lock_irq(get_ccwdev_lock(device->cdev));
         /* Setup callback */
         request->callback = __tape_wake_up;
-        request->callback_data = &wq;
+        request->callback_data = &device->wait_queue;
         /* Add request to request queue and try to start it. */
         rc = __tape_start_request(device, request);
         spin_unlock_irq(get_ccwdev_lock(device->cdev));
         if (rc)
                 return rc;
         /* Request added to the queue. Wait for its completion. */
-        wait_event(wq, (request->callback == NULL));
+        wait_event(device->wait_queue, (request->callback == NULL));
         /* Get rc from request */
         return request->rc;
 }
@@ -989,20 +988,19 @@ int
 tape_do_io_interruptible(struct tape_device *device,
                          struct tape_request *request)
 {
-        wait_queue_head_t wq;
         int rc;
 
-        init_waitqueue_head(&wq);
         spin_lock_irq(get_ccwdev_lock(device->cdev));
         /* Setup callback */
         request->callback = __tape_wake_up_interruptible;
-        request->callback_data = &wq;
+        request->callback_data = &device->wait_queue;
         rc = __tape_start_request(device, request);
         spin_unlock_irq(get_ccwdev_lock(device->cdev));
         if (rc)
                 return rc;
         /* Request added to the queue. Wait for its completion. */
-        rc = wait_event_interruptible(wq, (request->callback == NULL));
+        rc = wait_event_interruptible(device->wait_queue,
+                                      (request->callback == NULL));
         if (rc != -ERESTARTSYS)
                 /* Request finished normally. */
                 return request->rc;
@@ -1015,7 +1013,7 @@ tape_do_io_interruptible(struct tape_device *device,
                 /* Wait for the interrupt that acknowledges the halt. */
                 do {
                         rc = wait_event_interruptible(
-                                wq,
+                                device->wait_queue,
                                 (request->callback == NULL)
                         );
                 } while (rc == -ERESTARTSYS);