Jan Beulich
2010-Mar-01 09:25 UTC
[Xen-devel] [PATCH] linux/blktap2: Fwd: Re: Crash on blktap shutdown
Subject: blktap2: Fix queue restart, racing block device removal.
Makes tapdisk context test dev->gd before attempting a queue restart,
with the device lock held. Fixes a race lost against device
destruction, which may issued anywhere on the control path.
Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- a/drivers/xen/blktap2/device.c
+++ b/drivers/xen/blktap2/device.c
@@ -946,8 +946,6 @@
struct blktap_device *dev;
dev = &tap->device;
- if (!dev->gd || !dev->gd->queue)
- return;
if (blktap_active(tap) && RING_FULL(&tap->ring.ring)) {
blktap_defer(tap);
@@ -963,11 +961,15 @@
spin_lock_irq(&dev->lock);
/* Re-enable calldowns. */
- if (blk_queue_stopped(dev->gd->queue))
- blk_start_queue(dev->gd->queue);
+ if (dev->gd) {
+ struct request_queue *rq = dev->gd->queue;
- /* Kick things off immediately. */
- blktap_device_do_request(dev->gd->queue);
+ if (blk_queue_stopped(rq))
+ blk_start_queue(rq);
+
+ /* Kick things off immediately. */
+ blktap_device_do_request(rq);
+ }
spin_unlock_irq(&dev->lock);
}
@@ -1056,6 +1058,7 @@
blktap_device_destroy(struct blktap *tap)
{
struct blktap_device *dev = &tap->device;
+ struct gendisk *gd = dev->gd;
if (!test_bit(BLKTAP_DEVICE, &tap->dev_inuse))
return 0;
@@ -1067,8 +1070,9 @@
spin_lock_irq(&dev->lock);
/* No more blktap_device_do_request(). */
- blk_stop_queue(dev->gd->queue);
+ blk_stop_queue(gd->queue);
clear_bit(BLKTAP_DEVICE, &tap->dev_inuse);
+ dev->gd = NULL;
spin_unlock_irq(&dev->lock);
#ifdef ENABLE_PASSTHROUGH
@@ -1076,11 +1080,9 @@
blktap_device_close_bdev(tap);
#endif
- del_gendisk(dev->gd);
- blk_cleanup_queue(dev->gd->queue);
- put_disk(dev->gd);
-
- dev->gd = NULL;
+ del_gendisk(gd);
+ blk_cleanup_queue(gd->queue);
+ put_disk(gd);
wake_up(&tap->wq);
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