[Xen-devel] [PATCH 12/16] blkfront: Fix blkfront backend switch race (bdev open)

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Daniel Stodden <daniel.stodden@xxxxxxxxxx>

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>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 drivers/block/xen-blkfront.c |   25 ++++++++++++++++++++-----
 1 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 1046a58..974d59a 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1118,12 +1118,27 @@ 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;
+       struct gendisk *disk = bdev->bd_disk;
+       struct blkfront_info *info;
+       int err = 0;
 
-       if (!info->xbdev)
-               return -ENODEV;
-       info->users++;
-       return 0;
+       info = disk->private_data;
+       if (!info)
+               /* xbdev gone */
+               return -ERESTARTSYS;
+
+       mutex_lock(&info->mutex);
+
+       if (!info->gd)
+               /* xbdev is closed */
+               err = -ERESTARTSYS;
+
+       mutex_unlock(&info->mutex);
+
+       if (!err)
+               ++info->users;
+
+       return err;
 }
 
 static int blkif_release(struct gendisk *disk, fmode_t mode)
-- 
1.7.1.1


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