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From: Jeremy Fitzhardinge on 20 Jul 2010 16:50
From: Daniel Stodden <daniel.stodden(a)citrix.com>

We cannot read backend state within bdev operations, because it risks
grabbing the state change before xenbus gets to do it.

Fixed by tracking deferral with a frontend switch to Closing. State
exposure isn't strictly necessary, but the backends won't mind.

For a 'clean' deferral this seems actually a more decent protocol than
raising errors.

Signed-off-by: Daniel Stodden <daniel.stodden(a)citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge(a)citrix.com>
---
drivers/block/xen-blkfront.c | 46 ++++++++++++++++++++++++++++-------------
1 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 974d59a..214c92e 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1144,22 +1144,38 @@ static int blkif_open(struct block_device *bdev, fmode_t mode)
static int blkif_release(struct gendisk *disk, fmode_t mode)
{
struct blkfront_info *info = disk->private_data;
- info->users--;
- if (info->users == 0) {
- /* Check whether we have been instructed to close. We will
- have ignored this request initially, as the device was
- still mounted. */
- struct xenbus_device *dev = info->xbdev;
-
- if (!dev) {
- xlvbd_release_gendisk(info);
- kfree(info);
- } else if (xenbus_read_driver_state(dev->otherend)
- == XenbusStateClosing && info->is_ready) {
- xlvbd_release_gendisk(info);
- xenbus_frontend_closed(dev);
- }
+ struct block_device *bdev;
+ struct xenbus_device *xbdev;
+
+ if (--info->users)
+ return 0;
+
+ bdev = bdget_disk(disk, 0);
+ bdput(bdev);
+
+ /*
+ * Check if we have been instructed to close. We will have
+ * deferred this request, because the bdev was still open.
+ */
+
+ mutex_lock(&info->mutex);
+ xbdev = info->xbdev;
+
+ if (xbdev && xbdev->state == XenbusStateClosing) {
+ /* pending switch to state closed */
+ xlvbd_release_gendisk(info);
+ xenbus_frontend_closed(info->xbdev);
}
+
+ mutex_unlock(&info->mutex);
+
+ if (!xbdev) {
+ /* sudden device removal */
+ xlvbd_release_gendisk(info);
+ disk->private_data = NULL;
+ kfree(info);
+ }
+
return 0;
}

--
1.7.1.1

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