[PATCH 3.4 45/88] virtio-blk: Call del_gendisk() before disable guest kick

Greg Kroah-Hartman
2014-06-10T00:24:55Z

From: Asias He <asias@redhat.com>

commit 02e2b124943648fba0a2ccee5c3656a5653e0151 upstream.

del_gendisk() might not return due to failing to remove the
/sys/block/vda/serial sysfs entry when another thread (udev) is
trying to read it.

virtblk_remove()
vdev->config->reset() : guest will not kick us through interrupt
del_gendisk()
device_del()
kobject_del(): got stuck, sysfs entry ref count non zero

sysfs_open_file(): user space process read /sys/block/vda/serial
sysfs_get_active() : got sysfs entry ref count
dev_attr_show()
virtblk_serial_show()
blk_execute_rq() : got stuck, interrupt is disabled
request cannot be finished

This patch fixes it by calling del_gendisk() before we disable guest's
interrupt so that the request sent in virtblk_serial_show() will be
finished and del_gendisk() will success.

This fixes another race in hot-unplug process.

It is save to call del_gendisk(vblk->disk) before
flush_work(&vblk->config_work) which might access vblk->disk, because
vblk->disk is not freed until put_disk(vblk->disk).

Cc: virtualization@lists.linux-foundation.org
Cc: kvm@vger.kernel.org
Signed-off-by: Asias He <asias@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/virtio_blk.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -581,13 +581,13 @@ static void __devexit virtblk_remove(str
vblk->config_enable = false;
mutex_unlock(&vblk->config_lock);

+ del_gendisk(vblk->disk);
+
/* Stop all the virtqueues. */
vdev->config->reset(vdev);

flush_work(&vblk->config_work);

- del_gendisk(vblk->disk);
-
/* Abort requests dispatched to driver. */
spin_lock_irqsave(&vblk->lock, flags);
while ((vbr = virtqueue_detach_unused_buf(vblk->vq))) {