blktap2: Fix queue restart, racing block device removal.

Makes tapdisk context test dev->gd before attempting a queue restart,
with the device lock held. Fixes a race lost against device
destruction, which may issued anywhere on the control path.

Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@novell.com>

diff --git a/drivers/xen/blktap2/device.c b/drivers/xen/blktap2/device.c
index eb21e9683fc2c776f57c889fa8ef1820e92b2622..f15c72308cbfdd9cb9f3fcf16073012ba5378d40 100644 (file)
--- a/drivers/xen/blktap2/device.c
+++ b/drivers/xen/blktap2/device.c
@@ -951,8 +951,6 @@ blktap_device_restart(struct blktap *tap)
        struct blktap_device *dev;
 
        dev = &tap->device;
-       if (!dev->gd || !dev->gd->queue)
-               return;
 
        if (blktap_active(tap) && RING_FULL(&tap->ring.ring)) {
                blktap_defer(tap);
@@ -968,11 +966,15 @@ blktap_device_restart(struct blktap *tap)
        spin_lock_irq(&dev->lock);
 
        /* Re-enable calldowns. */
-       if (blk_queue_stopped(dev->gd->queue))
-               blk_start_queue(dev->gd->queue);
+       if (dev->gd) {
+               struct request_queue *rq = dev->gd->queue;
+
+               if (blk_queue_stopped(rq))
+                       blk_start_queue(rq);
 
-       /* Kick things off immediately. */
-       blktap_device_do_request(dev->gd->queue);
+               /* Kick things off immediately. */
+               blktap_device_do_request(rq);
+       }
 
        spin_unlock_irq(&dev->lock);
 }
@@ -1061,6 +1063,7 @@ int
 blktap_device_destroy(struct blktap *tap)
 {
        struct blktap_device *dev = &tap->device;
+       struct gendisk *gd = dev->gd;
 
        if (!test_bit(BLKTAP_DEVICE, &tap->dev_inuse))
                return 0;
@@ -1072,8 +1075,9 @@ blktap_device_destroy(struct blktap *tap)
 
        spin_lock_irq(&dev->lock);
        /* No more blktap_device_do_request(). */
-       blk_stop_queue(dev->gd->queue);
+       blk_stop_queue(gd->queue);
        clear_bit(BLKTAP_DEVICE, &tap->dev_inuse);
+       dev->gd = NULL;
        spin_unlock_irq(&dev->lock);
 
 #ifdef ENABLE_PASSTHROUGH
@@ -1081,11 +1085,9 @@ blktap_device_destroy(struct blktap *tap)
                blktap_device_close_bdev(tap);
 #endif
 
-       del_gendisk(dev->gd);
-       blk_cleanup_queue(dev->gd->queue);
-       put_disk(dev->gd);
-
-       dev->gd = NULL;
+       del_gendisk(gd);
+       blk_cleanup_queue(gd->queue);
+       put_disk(gd);
 
        wake_up(&tap->wq);