On 20.12.2012, at 12:38, Michael S. Tsirkin wrote:
> On Thu, Dec 20, 2012 at 12:27:53PM +0100, Alexander Graf wrote:
>>
>> On 20.12.2012, at 11:54, Michael S. Tsirkin wrote:
>>
>>> On Wed, Dec 19, 2012 at 08:40:15PM +0100, Alexander Graf wrote:
>>>> When a file system is mounted on a virtio-blk disk, we then remove it
>>>> and then reattach it, the reattached disk gets the same disk name and
>>>> ids as the hot removed one.
>>>>
>>>> This leads to very nasty effects - mostly rendering the newly attached
>>>> device completely unusable.
>>>>
>>>> Trying what happens when I do the same thing with a USB device, I saw
>>>> that the sd node simply doesn't get free'd when a device gets forcefully
>>>> removed.
>>>>
>>>> Imitate the same behavior for vd devices. This way broken vd devices
>>>> simply are never free'd and newly attached ones keep working just fine.
>>>>
>>>> Signed-off-by: Alexander Graf <agraf@xxxxxxx>
>>>> ---
>>>> drivers/block/virtio_blk.c | 7 ++++++-
>>>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>> index 0bdde8f..07a18e2 100644
>>>> --- a/drivers/block/virtio_blk.c
>>>> +++ b/drivers/block/virtio_blk.c
>>>> @@ -889,6 +889,7 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
>>>> {
>>>> struct virtio_blk *vblk = vdev->priv;
>>>> int index = vblk->index;
>>>> + int refc;
>>>>
>>>> /* Prevent config work handler from accessing the device. */
>>>> mutex_lock(&vblk->config_lock);
>>>> @@ -903,11 +904,15 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
>>>>
>>>> flush_work(&vblk->config_work);
>>>>
>>>> + refc = atomic_read(&disk_to_dev(vblk->disk)->kobj.kref.refcount);
>>>> put_disk(vblk->disk);
>>>> mempool_destroy(vblk->pool);
>>>> vdev->config->del_vqs(vdev);
>>>> kfree(vblk);
>>>> - ida_simple_remove(&vd_index_ida, index);
>>>> +
>>>> + /* Only free device id if we don't have any users */
>>>> + if (refc == 1)
>>>> + ida_simple_remove(&vd_index_ida, index);
>>>> }
>>>>
>>>> #ifdef CONFIG_PM
>>>
>>> Network devices take the approach of retrying every second.
>>> Donnu if it makes sense here.
>>
>> I would rather think the 100% right approach would be a recursive unrolling of all users bottom to top. Force unmount. Force close all fd's.
>> I'm not sure why that doesn't happen today, but it doesn't :).
>>
>>
>> Alex
>
> Especially force close fd's won't be easy. A simpler alternative
> would be preventing unplug by taking some reference count.
That's what happens when you do
<add>
mount /mnt
ls /mnt
<remove>
-- here remove failed for me --
But when you do
<add>
mount /mnt
<remove>
then remove works and we get the above problem.
I have to admit that I'm really not a big fan of preventing unplug though. In some cases, preventing simply doesn't work, for example when you unplug a USB stick or when your iscsi remote just vanishes.
Alex
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
