Re: [PATCH v7 3/3] tcm_vhost: Add hotplug/hotunplug support

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Apr 18, 2013 at 09:05:54AM +0800, Asias He wrote:
> In commit 365a7150094 ([SCSI] virtio-scsi: hotplug support for
> virtio-scsi), hotplug support is added to virtio-scsi.
> 
> This patch adds hotplug and hotunplug support to tcm_vhost.
> 
> You can create or delete a LUN in targetcli to hotplug or hotunplug a
> LUN in guest.
> 
> Changes in v7:
> - Add vhost_work_flush for vs->vs_event_work to this series
> 
> Changes in v6:
> - Pass tcm_vhost_evt to tcm_vhost_do_evt_work
> 
> Changes in v5:
> - Switch to int from u64 to vs_events_nr
> - Set s->vs_events_dropped flag in tcm_vhost_allocate_evt
> - Do not nest dev mutex within vq mutex
> - Use vs_events_lock to protect vs_events_dropped and vs_events_nr
> - Rebase to target/master
> 
> Changes in v4:
> - Drop tcm_vhost_check_endpoint in tcm_vhost_send_evt
> - Add tcm_vhost_check_endpoint in vhost_scsi_evt_handle_kick
> 
> Changes in v3:
> - Separate the bug fix to another thread
> 
> Changes in v2:
> - Remove code duplication in tcm_vhost_{hotplug,hotunplug}
> - Fix racing of vs_events_nr
> - Add flush fix patch to this series
> 
> Signed-off-by: Asias He <asias@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  drivers/vhost/tcm_vhost.c | 208 +++++++++++++++++++++++++++++++++++++++++++++-
>  drivers/vhost/tcm_vhost.h |  10 +++
>  2 files changed, 214 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> index 8f05528..da2021b 100644
> --- a/drivers/vhost/tcm_vhost.c
> +++ b/drivers/vhost/tcm_vhost.c
> @@ -66,11 +66,13 @@ enum {
>   * TODO: debug and remove the workaround.
>   */
>  enum {
> -	VHOST_SCSI_FEATURES = VHOST_FEATURES & (~VIRTIO_RING_F_EVENT_IDX)
> +	VHOST_SCSI_FEATURES = (VHOST_FEATURES & (~VIRTIO_RING_F_EVENT_IDX)) |
> +			      (1ULL << VIRTIO_SCSI_F_HOTPLUG)
>  };
>  
>  #define VHOST_SCSI_MAX_TARGET	256
>  #define VHOST_SCSI_MAX_VQ	128
> +#define VHOST_SCSI_MAX_EVENT	128
>  
>  struct vhost_scsi {
>  	/* Protected by vhost_scsi->dev.mutex */
> @@ -82,6 +84,13 @@ struct vhost_scsi {
>  
>  	struct vhost_work vs_completion_work; /* cmd completion work item */
>  	struct llist_head vs_completion_list; /* cmd completion queue */
> +
> +	struct vhost_work vs_event_work; /* evt injection work item */
> +	struct llist_head vs_event_list; /* evt injection queue */
> +
> +	struct mutex vs_events_lock; /* protect vs_events_dropped,events_nr */

Looking at this code, there are just so many locks now.
This does not make me feel safe :)
At least, please document lock nesting.


> +	bool vs_events_dropped; /* any missed events */
> +	int vs_events_nr; /* num of pending events */
>  };
>  
>  /* Local pointer to allocated TCM configfs fabric module */
> @@ -129,6 +138,17 @@ static bool tcm_vhost_check_endpoint(struct vhost_virtqueue *vq)
>  	return ret;
>  }
>  
> +static bool tcm_vhost_check_events_dropped(struct vhost_scsi *vs)
> +{
> +	bool ret;
> +
> +	mutex_lock(&vs->vs_events_lock);
> +	ret = vs->vs_events_dropped;
> +	mutex_unlock(&vs->vs_events_lock);
> +
> +	return ret;
> +}
> +
>  static int tcm_vhost_check_true(struct se_portal_group *se_tpg)
>  {
>  	return 1;
> @@ -379,6 +399,37 @@ static int tcm_vhost_queue_tm_rsp(struct se_cmd *se_cmd)
>  	return 0;
>  }
>  
> +static void tcm_vhost_free_evt(struct vhost_scsi *vs, struct tcm_vhost_evt *evt)
> +{
> +	mutex_lock(&vs->vs_events_lock);
> +	vs->vs_events_nr--;
> +	kfree(evt);
> +	mutex_unlock(&vs->vs_events_lock);
> +}
> +
> +static struct tcm_vhost_evt *tcm_vhost_allocate_evt(struct vhost_scsi *vs,
> +	u32 event, u32 reason)
> +{
> +	struct tcm_vhost_evt *evt;
> +
> +	mutex_lock(&vs->vs_events_lock);
> +	if (vs->vs_events_nr > VHOST_SCSI_MAX_EVENT) {
> +		vs->vs_events_dropped = true;
> +		mutex_unlock(&vs->vs_events_lock);
> +		return NULL;
> +	}
> +
> +	evt = kzalloc(sizeof(*evt), GFP_KERNEL);

I think kzalloc not needed here, you init all fields.

Also, this basically means if backend does plug/unplug very quickly,
we start consuming kernel memory without a limit. Not good.
How about we allocate the event as part of target?
There shouldn't ever be more than one hotplug
event in flight per target, right?


> +	if (evt) {

Let's do clean error handling here and above:
if (!evt)
	goto err;

> +		evt->event.event = event;
> +		evt->event.reason = reason;
> +		vs->vs_events_nr++;
> +	}
> +	mutex_unlock(&vs->vs_events_lock);
> +
> +	return evt;
> +}
> +
>  static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
>  {
>  	struct se_cmd *se_cmd = &tv_cmd->tvc_se_cmd;
> @@ -397,6 +448,75 @@ static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
>  	kfree(tv_cmd);
>  }
>  
> +static void tcm_vhost_do_evt_work(struct vhost_scsi *vs,
> +	struct tcm_vhost_evt *evt)
> +{
> +	struct vhost_virtqueue *vq = &vs->vqs[VHOST_SCSI_VQ_EVT];
> +	struct virtio_scsi_event *event = &evt->event;
> +	struct virtio_scsi_event __user *eventp;
> +	unsigned out, in;
> +	int head, ret;
> +
> +	if (!tcm_vhost_check_endpoint(vq))
> +		return;
> +
> +	mutex_lock(&vs->vs_events_lock);
> +	mutex_lock(&vq->mutex);
> +again:
> +	vhost_disable_notify(&vs->dev, vq);
> +	head = vhost_get_vq_desc(&vs->dev, vq, vq->iov,
> +			ARRAY_SIZE(vq->iov), &out, &in,
> +			NULL, NULL);
> +	if (head < 0) {
> +		vs->vs_events_dropped = true;
> +		goto out;
> +	}
> +	if (head == vq->num) {
> +		if (vhost_enable_notify(&vs->dev, vq))
> +			goto again;

Please write loops with while() or for().
Not with goto. goto is for error handling.

> +		vs->vs_events_dropped = true;
> +		goto out;
> +	}
> +
> +	if ((vq->iov[out].iov_len != sizeof(struct virtio_scsi_event))) {
> +		vq_err(vq, "Expecting virtio_scsi_event, got %zu bytes\n",
> +				vq->iov[out].iov_len);
> +		vs->vs_events_dropped = true;
> +		goto out;
> +	}
> +
> +	if (vs->vs_events_dropped) {
> +		event->event |= VIRTIO_SCSI_T_EVENTS_MISSED;
> +		vs->vs_events_dropped = false;
> +	}
> +
> +	eventp = vq->iov[out].iov_base;
> +	ret = __copy_to_user(eventp, event, sizeof(*event));
> +	if (!ret)
> +		vhost_add_used_and_signal(&vs->dev, vq, head, 0);
> +	else
> +		vq_err(vq, "Faulted on tcm_vhost_send_event\n");
> +out:
> +	mutex_unlock(&vq->mutex);
> +	mutex_unlock(&vs->vs_events_lock);
> +}
> +
> +static void tcm_vhost_evt_work(struct vhost_work *work)
> +{
> +	struct vhost_scsi *vs = container_of(work, struct vhost_scsi,
> +					vs_event_work);
> +	struct tcm_vhost_evt *evt;
> +	struct llist_node *llnode;
> +
> +	llnode = llist_del_all(&vs->vs_event_list);

The assumption is that this is slow path thing, no need to worry about
speed, yes? so let's do simple list_add, list_del etc.

> +	while (llnode) {
> +		evt = llist_entry(llnode, struct tcm_vhost_evt, list);
> +		llnode = llist_next(llnode);
> +		tcm_vhost_do_evt_work(vs, evt);
> +		tcm_vhost_free_evt(vs, evt);
> +	}
> +}
> +
>  /* Fill in status and signal that we are done processing this command
>   *
>   * This is scheduled in the vhost work queue so we are called with the owner
> @@ -807,9 +927,42 @@ static void vhost_scsi_ctl_handle_kick(struct vhost_work *work)
>  	pr_debug("%s: The handling func for control queue.\n", __func__);
>  }
>  
> +static int tcm_vhost_send_evt(struct vhost_scsi *vs, struct tcm_vhost_tpg *tpg,
> +	struct se_lun *lun, u32 event, u32 reason)
> +{
> +	struct tcm_vhost_evt *evt;
> +
> +	evt = tcm_vhost_allocate_evt(vs, event, reason);
> +	if (!evt)
> +		return -ENOMEM;
> +
> +	if (tpg && lun) {
> +		/* TODO: share lun setup code with virtio-scsi.ko */
> +		evt->event.lun[0] = 0x01;
> +		evt->event.lun[1] = tpg->tport_tpgt & 0xFF;
> +		if (lun->unpacked_lun >= 256)
> +			evt->event.lun[2] = lun->unpacked_lun >> 8 | 0x40 ;
> +		evt->event.lun[3] = lun->unpacked_lun & 0xFF;
> +	}
> +
> +	llist_add(&evt->list, &vs->vs_event_list);
> +	vhost_work_queue(&vs->dev, &vs->vs_event_work);
> +
> +	return 0;
> +}
> +
>  static void vhost_scsi_evt_handle_kick(struct vhost_work *work)
>  {
> -	pr_debug("%s: The handling func for event queue.\n", __func__);
> +	struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
> +						poll.work);
> +	struct vhost_scsi *vs = container_of(vq->dev, struct vhost_scsi, dev);
> +
> +	if (!tcm_vhost_check_endpoint(vq))
> +		return;

Again just drop this check.

> +
> +	if (tcm_vhost_check_events_dropped(vs))
> +		tcm_vhost_send_evt(vs, NULL, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
> +
>  }
>  
>  static void vhost_scsi_handle_kick(struct vhost_work *work)
> @@ -833,6 +986,7 @@ static void vhost_scsi_flush(struct vhost_scsi *vs)
>  	for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
>  		vhost_scsi_flush_vq(vs, i);
>  	vhost_work_flush(&vs->dev, &vs->vs_completion_work);
> +	vhost_work_flush(&vs->dev, &vs->vs_event_work);
>  }
>  
>  /*
> @@ -891,6 +1045,7 @@ static int vhost_scsi_set_endpoint(
>  				return -EEXIST;
>  			}
>  			tv_tpg->tv_tpg_vhost_count++;
> +			tv_tpg->vhost_scsi = vs;
>  			vs_tpg[tv_tpg->tport_tpgt] = tv_tpg;
>  			smp_mb__after_atomic_inc();
>  			match = true;
> @@ -974,6 +1129,7 @@ static int vhost_scsi_clear_endpoint(
>  			goto err_tpg;
>  		}
>  		tv_tpg->tv_tpg_vhost_count--;
> +		tv_tpg->vhost_scsi = NULL;
>  		vs->vs_tpg[target] = NULL;
>  		match = true;
>  		mutex_unlock(&tv_tpg->tv_tpg_mutex);
> @@ -1033,6 +1189,11 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
>  		return -ENOMEM;
>  
>  	vhost_work_init(&s->vs_completion_work, vhost_scsi_complete_cmd_work);
> +	vhost_work_init(&s->vs_event_work, tcm_vhost_evt_work);
> +
> +	s->vs_events_nr = 0;
> +	s->vs_events_dropped = false;
> +	mutex_init(&s->vs_events_lock);
>  
>  	s->vqs[VHOST_SCSI_VQ_CTL].handle_kick = vhost_scsi_ctl_handle_kick;
>  	s->vqs[VHOST_SCSI_VQ_EVT].handle_kick = vhost_scsi_evt_handle_kick;
> @@ -1163,6 +1324,42 @@ static char *tcm_vhost_dump_proto_id(struct tcm_vhost_tport *tport)
>  	return "Unknown";
>  }
>  
> +static int tcm_vhost_do_plug(struct tcm_vhost_tpg *tpg,
> +	struct se_lun *lun, bool plug)
> +{
> +
> +	struct vhost_scsi *vs = tpg->vhost_scsi;
> +	u32 reason;
> +
> +	mutex_lock(&tpg->tv_tpg_mutex);
> +	vs = tpg->vhost_scsi;
> +	mutex_unlock(&tpg->tv_tpg_mutex);
> +	if (!vs)
> +		return -EOPNOTSUPP;

Why EOPNOTSUPP? When does this happen?

> +
> +	if (!tcm_vhost_check_feature(vs, VIRTIO_SCSI_F_HOTPLUG))
> +		return -EOPNOTSUPP;
> +
> +	if (plug)
> +		reason = VIRTIO_SCSI_EVT_RESET_RESCAN;
> +	else
> +		reason = VIRTIO_SCSI_EVT_RESET_REMOVED;
> +

You have dropped the tpg lock so tpg->vhost_scsi can become
NULL now. Why is this safe?

> +	return tcm_vhost_send_evt(vs, tpg, lun,
> +			VIRTIO_SCSI_T_TRANSPORT_RESET,
> +			reason);
> +}
> +
> +static int tcm_vhost_hotplug(struct tcm_vhost_tpg *tpg, struct se_lun *lun)
> +{
> +	return tcm_vhost_do_plug(tpg, lun, true);
> +}
> +
> +static int tcm_vhost_hotunplug(struct tcm_vhost_tpg *tpg, struct se_lun *lun)
> +{
> +	return tcm_vhost_do_plug(tpg, lun, false);
> +}
> +

What are these wrappers for? Seem useless ...

>  static int tcm_vhost_port_link(struct se_portal_group *se_tpg,
>  	struct se_lun *lun)
>  {
> @@ -1173,18 +1370,21 @@ static int tcm_vhost_port_link(struct se_portal_group *se_tpg,
>  	tv_tpg->tv_tpg_port_count++;
>  	mutex_unlock(&tv_tpg->tv_tpg_mutex);
>  
> +	tcm_vhost_hotplug(tv_tpg, lun);
> +
>  	return 0;
>  }
>  
>  static void tcm_vhost_port_unlink(struct se_portal_group *se_tpg,
> -	struct se_lun *se_lun)
> +	struct se_lun *lun)
>  {
>  	struct tcm_vhost_tpg *tv_tpg = container_of(se_tpg,
>  				struct tcm_vhost_tpg, se_tpg);
> -
>  	mutex_lock(&tv_tpg->tv_tpg_mutex);
>  	tv_tpg->tv_tpg_port_count--;
>  	mutex_unlock(&tv_tpg->tv_tpg_mutex);
> +
> +	tcm_vhost_hotunplug(tv_tpg, lun);
>  }
>  
>  static struct se_node_acl *tcm_vhost_make_nodeacl(
> diff --git a/drivers/vhost/tcm_vhost.h b/drivers/vhost/tcm_vhost.h
> index 1d2ae7a..94e9ee53 100644
> --- a/drivers/vhost/tcm_vhost.h
> +++ b/drivers/vhost/tcm_vhost.h
> @@ -53,6 +53,7 @@ struct tcm_vhost_nacl {
>  	struct se_node_acl se_node_acl;
>  };
>  
> +struct vhost_scsi;
>  struct tcm_vhost_tpg {
>  	/* Vhost port target portal group tag for TCM */
>  	u16 tport_tpgt;
> @@ -70,6 +71,8 @@ struct tcm_vhost_tpg {
>  	struct tcm_vhost_tport *tport;
>  	/* Returned by tcm_vhost_make_tpg() */
>  	struct se_portal_group se_tpg;
> +	/* Pointer back to struct vhost_scsi, protected by tv_tpg_mutex */
> +	struct vhost_scsi *vhost_scsi;
>  };
>  
>  struct tcm_vhost_tport {
> @@ -83,6 +86,13 @@ struct tcm_vhost_tport {
>  	struct se_wwn tport_wwn;
>  };
>  
> +struct tcm_vhost_evt {
> +	/* virtio_scsi event */
> +	struct virtio_scsi_event event;
> +	/* virtio_scsi event list, serviced from vhost worker thread */
> +	struct llist_node list;
> +};
> +
>  /*
>   * As per request from MST, keep TCM_VHOST related ioctl defines out of
>   * linux/vhost.h (user-space) for now..
> -- 
> 1.8.1.4