blkfront: Fix blkfront backend switch race (bdev open)

We need not mind if users grab a late handle on a closing disk. We
probably even should not. But we have to make sure it's not a dead
one already

Let the bdev deal with a gendisk deleted under its feet. Takes the
info mutex to decide a race against backend closing.

Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 1e406f0331e707a848467c4db219f6613bc250bb..763a315712cc9a506e81832f6d53eba90d7be161 100644 (file)
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1118,16 +1118,33 @@ static int blkfront_is_ready(struct xenbus_device *dev)
 
 static int blkif_open(struct block_device *bdev, fmode_t mode)
 {
-       struct blkfront_info *info = bdev->bd_disk->private_data;
-
-       if (!info->xbdev)
-               return -ENODEV;
+       struct gendisk *disk = bdev->bd_disk;
+       struct blkfront_info *info;
+       int err = 0;
 
        lock_kernel();
-       info->users++;
-       unlock_kernel();
 
-       return 0;
+       info = disk->private_data;
+       if (!info) {
+               /* xbdev gone */
+               err = -ERESTARTSYS;
+               goto out;
+       }
+
+       mutex_lock(&info->mutex);
+
+       if (!info->gd)
+               /* xbdev is closed */
+               err = -ERESTARTSYS;
+
+       mutex_unlock(&info->mutex);
+
+       if (!err)
+               ++info->users;
+
+       unlock_kernel();
+out:
+       return err;
 }
 
 static int blkif_release(struct gendisk *disk, fmode_t mode)