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blkfront: Lock blkfront_info when closing

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The bdev .open/.release fops race against backend switches to Closing,
handled by the XenBus thread.

The original code attempted to serialize block device holders and
xenbus only via bd_mutex. This is insufficient, the info->bd pointer
may already be stale (or null) while xenbus tries to bump up the
refcount.

Protect blkfront_info with a dedicated mutex.

Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
This commit is contained in:
Daniel Stodden 2010-04-30 22:01:19 +00:00 committed by Jens Axboe
parent a66b5aebb7
commit b70f5fa043
1 changed files with 40 additions and 21 deletions
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61
drivers/block/xen-blkfront.c
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@ -79,6 +79,7 @@ static const struct block_device_operations xlvbd_block_fops;
*/
struct blkfront_info
{
struct mutex mutex;
struct xenbus_device *xbdev;
struct gendisk *gd;
int vdevice;
@ -804,7 +805,6 @@ again:
return err;
}
/**
* Entry point to this code when a new device is created. Allocate the basic
* structures and the ring buffer for communication with the backend, and
@ -836,6 +836,7 @@ static int blkfront_probe(struct xenbus_device *dev,
return -ENOMEM;
}
mutex_init(&info->mutex);
info->xbdev = dev;
info->vdevice = vdevice;
info->connected = BLKIF_STATE_DISCONNECTED;
@ -951,6 +952,43 @@ static int blkfront_resume(struct xenbus_device *dev)
return err;
}
static void
blkfront_closing(struct blkfront_info *info)
{
struct xenbus_device *xbdev = info->xbdev;
struct block_device *bdev = NULL;
mutex_lock(&info->mutex);
if (xbdev->state == XenbusStateClosing) {
mutex_unlock(&info->mutex);
return;
}
if (info->gd)
bdev = bdget_disk(info->gd, 0);
mutex_unlock(&info->mutex);
if (!bdev) {
xenbus_frontend_closed(xbdev);
return;
}
mutex_lock(&bdev->bd_mutex);
if (info->users) {
xenbus_dev_error(xbdev, -EBUSY,
"Device in use; refusing to close");
xenbus_switch_state(xbdev, XenbusStateClosing);
} else {
xlvbd_release_gendisk(info);
xenbus_frontend_closed(xbdev);
}
mutex_unlock(&bdev->bd_mutex);
bdput(bdev);
}
/*
* Invoked when the backend is finally 'ready' (and has told produced
@ -1034,7 +1072,6 @@ static void blkback_changed(struct xenbus_device *dev,
enum xenbus_state backend_state)
{
struct blkfront_info *info = dev_get_drvdata(&dev->dev);
struct block_device *bd;
dev_dbg(&dev->dev, "blkfront:blkback_changed to state %d.\n", backend_state);
@ -1051,25 +1088,7 @@ static void blkback_changed(struct xenbus_device *dev,
break;
case XenbusStateClosing:
if (info->gd == NULL) {
xenbus_frontend_closed(dev);
break;
}
bd = bdget_disk(info->gd, 0);
if (bd == NULL)
xenbus_dev_fatal(dev, -ENODEV, "bdget failed");
mutex_lock(&bd->bd_mutex);
if (info->users > 0)
xenbus_dev_error(dev, -EBUSY,
"Device in use; refusing to close");
else {
xlvbd_release_gendisk(info);
xenbus_frontend_closed(info->xbdev);
}
mutex_unlock(&bd->bd_mutex);
bdput(bd);
blkfront_closing(info);
break;
}
}