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Subject[PATCH 12/16] blkfront: Fix blkfront backend switch race (bdev open)
Date
From: Daniel Stodden <daniel.stodden@citrix.com>

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>
---
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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