[Xen-devel] [PATCH] linux/blktap2: Fwd: Re: Crash on blktap shutdown

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

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@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 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);

Attachment: blktap2-queue-restart-race.patch
Description: Text document

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