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blkfront: Fix blkfront backend switch race (bdev release)

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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@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Daniel Stodden 2010-08-07 18:45:12 +02:00 committed by Jens Axboe
parent 139617437a
commit 7fd152f4b6
1 changed files with 33 additions and 16 deletions
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49
drivers/block/xen-blkfront.c
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@ -1142,31 +1142,48 @@ static int blkif_open(struct block_device *bdev, fmode_t mode)
if (!err)
++info->users;
unlock_kernel();
out:
unlock_kernel();
return err;
}
static int blkif_release(struct gendisk *disk, fmode_t mode)
{
struct blkfront_info *info = disk->private_data;
lock_kernel();
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;
struct block_device *bdev;
struct xenbus_device *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);
}
lock_kernel();
if (--info->users)
goto out;
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);
}
out:
unlock_kernel();
return 0;
}