# HG changeset patch
# User Daniel Stodden <daniel.stodden@xxxxxxxxxx>
# Date 1272506749 25200
# Node ID 5e73c8d7aaf5bff5caa7d431184ffed8e837997a
# Parent  6a52e76a65073a521d531d875d141b1e89a38954
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@xxxxxxxxxx>

diff -r 6a52e76a6507 -r 5e73c8d7aaf5 drivers/block/xen-blkfront.c
--- a/drivers/block/xen-blkfront.c	Wed Apr 28 19:05:49 2010 -0700
+++ b/drivers/block/xen-blkfront.c	Wed Apr 28 19:05:49 2010 -0700
@@ -1100,12 +1100,23 @@
 
 static int blkif_open(struct block_device *bdev, fmode_t mode)
 {
-	struct blkfront_info *info = bdev->bd_disk->private_data;
+	struct gendisk *disk = bdev->bd_disk;
+	struct blkfront_info *info = disk->private_data;
+	int err = 0;
 
-	if (!info->xbdev)
-		return -ENODEV;
-	info->users++;
-	return 0;
+	mutex_lock(&info->mutex);
+	/*
+	 * Let the bdev deal with a gendisk deleted under its feet.
+	 */
+	if (!info->gd)
+		err = -ERESTARTSYS;
+
+	mutex_unlock(&info->mutex);
+
+	if (!err)
+		++info->users;
+
+	return err;
 }
 
 static int blkif_release(struct gendisk *disk, fmode_t mode)