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blkfront: Fix blkfront backend switch race (bdev release) 

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
View File

@ -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;
}