virtio-blk: Call del_gendisk() before disable guest kick
authorAsias He <asias@redhat.com>
Fri, 25 May 2012 02:34:47 +0000 (10:34 +0800)
committerRusty Russell <rusty@rustcorp.com.au>
Mon, 30 Jul 2012 04:00:51 +0000 (13:30 +0930)
commit02e2b124943648fba0a2ccee5c3656a5653e0151
treed93d06c9d3ba8c94015017040c0c5c7185f3ffc3
parent0bc1a2ef19b45bb23617b203bc631b44609f17ba
virtio-blk: Call del_gendisk() before disable guest kick

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
Cc: stable@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>
drivers/block/virtio_blk.c