On Fri, May 25, 2012 at 10:34:47AM +0800, Asias He wrote:
> 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: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx
> Signed-off-by: Asias He <asias@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/block/virtio_blk.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 693187d..1bed517 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -584,13 +584,13 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
> 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))) {
> --
> 1.7.10.2
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