Re: [PATCH] tcm_vhost: Wait for pending requests in vhost_scsi_flush()

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

On Tue, Apr 09, 2013 at 05:39:43PM +0800, Asias He wrote:
> This patch makes vhost_scsi_flush() wait for all the pending requests
> issued before the flush operation to be finished.
> 
> Changes in v3:
> - Rebase
> - Drop 'tcm_vhost: Wait for pending requests in
>   vhost_scsi_clear_endpoint()' in this series, we already did that in
>   'tcm_vhost: Use vq->private_data to indicate if the endpoint is setup'
> 
> Changes in v2:
> - Increase/Decrease inflight requests in
>   vhost_scsi_{allocate,free}_cmd and tcm_vhost_{allocate,free}_evt
> 
> Signed-off-by: Asias He <asias@redhat.com>

Nack, let's not do this home-grown here.  Please use a kref.

The array of two trick is also too tricky for my taste.

Please replace during_flush in tcm_vhost_cmd and tcm_vhost_evt
by a kref pointer, allocate a new kref when you flush.

Access can be done with RCU so we won't need any locks.

> ---
>  drivers/vhost/tcm_vhost.c | 88 ++++++++++++++++++++++++++++++++++++++++++++---
>  drivers/vhost/tcm_vhost.h |  4 +++
>  2 files changed, 87 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> index 1f9116c..719ce13 100644
> --- a/drivers/vhost/tcm_vhost.c
> +++ b/drivers/vhost/tcm_vhost.c
> @@ -91,6 +91,15 @@ struct vhost_scsi {
>  	struct mutex vs_events_lock; /* protect vs_events_dropped,events_nr */
>  	bool vs_events_dropped; /* any missed events */
>  	int vs_events_nr; /* num of pending events */
> +
> +	/*
> +	 * vs_inflight[0]/[1] are used to track requests issued
> +	 * before/during the flush operation
> +	 */
> +	u64 vs_inflight[2];
> +	wait_queue_head_t vs_flush_wait; /* wait queue for flush operation */
> +	spinlock_t vs_flush_lock; /* lock to protect vs_during_flush */
> +	int vs_during_flush; /* flag to indicate if we are in flush operation */
>  };
>  
>  /* Local pointer to allocated TCM configfs fabric module */
> @@ -108,6 +117,46 @@ static int iov_num_pages(struct iovec *iov)
>  	       ((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT;
>  }
>  
> +static int tcm_vhost_inc_inflight(struct vhost_scsi *vs)
> +{
> +	int during_flush;
> +
> +	spin_lock(&vs->vs_flush_lock);
> +	during_flush = vs->vs_during_flush;
> +	vs->vs_inflight[during_flush]++;
> +	spin_unlock(&vs->vs_flush_lock);
> +
> +	return during_flush;
> +}
> +
> +static void tcm_vhost_dec_inflight(struct vhost_scsi *vs, int during_flush)
> +{
> +	u64 inflight;
> +
> +	spin_lock(&vs->vs_flush_lock);
> +	inflight = vs->vs_inflight[during_flush]--;
> +	/*
> +	 * Wakeup the waiter when all the requests issued before the flush
> +	 * operation are finished and we are during the flush operation.
> +	 */
> +	if (!inflight && !during_flush && vs->vs_during_flush)
> +		wake_up(&vs->vs_flush_wait);
> +	spin_unlock(&vs->vs_flush_lock);
> +}
> +
> +static bool tcm_vhost_done_inflight(struct vhost_scsi *vs)
> +{
> +	bool ret = false;
> +
> +	/* The requests issued before the flush operation are finished ? */
> +	spin_lock(&vs->vs_flush_lock);
> +	if (!vs->vs_inflight[0])
> +		ret = true;
> +	spin_unlock(&vs->vs_flush_lock);
> +
> +	return ret;
> +}
> +
>  static bool tcm_vhost_check_feature(struct vhost_scsi *vs, int feature)
>  {
>  	bool ret = false;
> @@ -402,6 +451,7 @@ static int tcm_vhost_queue_tm_rsp(struct se_cmd *se_cmd)
>  static void tcm_vhost_free_evt(struct vhost_scsi *vs, struct tcm_vhost_evt *evt)
>  {
>  	mutex_lock(&vs->vs_events_lock);
> +	tcm_vhost_dec_inflight(vs, evt->during_flush);
>  	vs->vs_events_nr--;
>  	kfree(evt);
>  	mutex_unlock(&vs->vs_events_lock);
> @@ -423,6 +473,7 @@ static struct tcm_vhost_evt *tcm_vhost_allocate_evt(struct vhost_scsi *vs,
>  	if (evt) {
>  		evt->event.event = event;
>  		evt->event.reason = reason;
> +		evt->during_flush = tcm_vhost_inc_inflight(vs);
>  		vs->vs_events_nr++;
>  	}
>  	mutex_unlock(&vs->vs_events_lock);
> @@ -433,6 +484,7 @@ static struct tcm_vhost_evt *tcm_vhost_allocate_evt(struct vhost_scsi *vs,
>  static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
>  {
>  	struct se_cmd *se_cmd = &tv_cmd->tvc_se_cmd;
> +	struct vhost_scsi *vs = tv_cmd->tvc_vhost;
>  
>  	/* TODO locking against target/backend threads? */
>  	transport_generic_free_cmd(se_cmd, 1);
> @@ -445,13 +497,16 @@ static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
>  		kfree(tv_cmd->tvc_sgl);
>  	}
>  
> +	tcm_vhost_dec_inflight(vs, tv_cmd->during_flush);
> +
>  	kfree(tv_cmd);
>  }
>  
>  static void tcm_vhost_do_evt_work(struct vhost_scsi *vs,
> -	struct virtio_scsi_event *event)
> +	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;
> @@ -511,7 +566,7 @@ static void tcm_vhost_evt_work(struct vhost_work *work)
>  	while (llnode) {
>  		evt = llist_entry(llnode, struct tcm_vhost_evt, list);
>  		llnode = llist_next(llnode);
> -		tcm_vhost_do_evt_work(vs, &evt->event);
> +		tcm_vhost_do_evt_work(vs, evt);
>  		tcm_vhost_free_evt(vs, evt);
>  	}
>  }
> @@ -529,8 +584,8 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
>  	struct virtio_scsi_cmd_resp v_rsp;
>  	struct tcm_vhost_cmd *tv_cmd;
>  	struct llist_node *llnode;
> -	struct se_cmd *se_cmd;
>  	int ret, vq;
> +	struct se_cmd *se_cmd;
>  
>  	bitmap_zero(signal, VHOST_SCSI_MAX_VQ);
>  	llnode = llist_del_all(&vs->vs_completion_list);
> @@ -568,6 +623,7 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
>  }
>  
>  static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
> +	struct vhost_scsi *vs,
>  	struct tcm_vhost_tpg *tv_tpg,
>  	struct virtio_scsi_cmd_req *v_req,
>  	u32 exp_data_len,
> @@ -592,6 +648,8 @@ static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
>  	tv_cmd->tvc_exp_data_len = exp_data_len;
>  	tv_cmd->tvc_data_direction = data_direction;
>  	tv_cmd->tvc_nexus = tv_nexus;
> +	tv_cmd->tvc_vhost = vs;
> +	tv_cmd->during_flush = tcm_vhost_inc_inflight(vs);
>  
>  	return tv_cmd;
>  }
> @@ -842,7 +900,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
>  		for (i = 0; i < data_num; i++)
>  			exp_data_len += vq->iov[data_first + i].iov_len;
>  
> -		tv_cmd = vhost_scsi_allocate_cmd(tv_tpg, &v_req,
> +		tv_cmd = vhost_scsi_allocate_cmd(vs, tv_tpg, &v_req,
>  					exp_data_len, data_direction);
>  		if (IS_ERR(tv_cmd)) {
>  			vq_err(vq, "vhost_scsi_allocate_cmd failed %ld\n",
> @@ -852,7 +910,6 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
>  		pr_debug("Allocated tv_cmd: %p exp_data_len: %d, data_direction"
>  			": %d\n", tv_cmd, exp_data_len, data_direction);
>  
> -		tv_cmd->tvc_vhost = vs;
>  		tv_cmd->tvc_vq = vq;
>  
>  		if (unlikely(vq->iov[out].iov_len !=
> @@ -905,6 +962,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
>  		 * tcm_vhost_queue_data_in() and tcm_vhost_queue_status()
>  		 */
>  		tv_cmd->tvc_vq_desc = head;
> +
>  		/*
>  		 * Dispatch tv_cmd descriptor for cmwq execution in process
>  		 * context provided by tcm_vhost_workqueue.  This also ensures
> @@ -984,9 +1042,23 @@ static void vhost_scsi_flush(struct vhost_scsi *vs)
>  {
>  	int i;
>  
> +	/* Flush operation is started */
> +	spin_lock(&vs->vs_flush_lock);
> +	vs->vs_during_flush = 1;
> +	spin_unlock(&vs->vs_flush_lock);
> +
>  	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);
> +
> +	/* Wait until all requests issued before the flush to be finished */
> +	wait_event(vs->vs_flush_wait, tcm_vhost_done_inflight(vs));
> +
> +	/* Flush operation is finished */
> +	spin_lock(&vs->vs_flush_lock);
> +	vs->vs_during_flush = 0;
> +	spin_unlock(&vs->vs_flush_lock);
>  }
>  
>  /*
> @@ -1094,6 +1166,7 @@ static int vhost_scsi_clear_endpoint(
>  	u8 target;
>  
>  	mutex_lock(&vs->dev.mutex);
> +
>  	/* Verify that ring has been setup correctly. */
>  	for (index = 0; index < vs->dev.nvqs; ++index) {
>  		if (!vhost_vq_access_ok(&vs->vqs[index])) {
> @@ -1195,6 +1268,11 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
>  	s->vs_events_dropped = false;
>  	mutex_init(&s->vs_events_lock);
>  
> +	s->vs_inflight[0] = 0;
> +	s->vs_inflight[1] = 0;
> +	spin_lock_init(&s->vs_flush_lock);
> +	init_waitqueue_head(&s->vs_flush_wait);
> +
>  	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;
>  	for (i = VHOST_SCSI_VQ_IO; i < VHOST_SCSI_MAX_VQ; i++)
> diff --git a/drivers/vhost/tcm_vhost.h b/drivers/vhost/tcm_vhost.h
> index 94e9ee53..dd84622 100644
> --- a/drivers/vhost/tcm_vhost.h
> +++ b/drivers/vhost/tcm_vhost.h
> @@ -37,6 +37,8 @@ struct tcm_vhost_cmd {
>  	unsigned char tvc_sense_buf[TRANSPORT_SENSE_BUFFER];
>  	/* Completed commands list, serviced from vhost worker thread */
>  	struct llist_node tvc_completion_list;
> +	/* Indicate this command is issued during the flush operaton */
> +	int during_flush;
>  };
>  
>  struct tcm_vhost_nexus {
> @@ -91,6 +93,8 @@ struct tcm_vhost_evt {
>  	struct virtio_scsi_event event;
>  	/* virtio_scsi event list, serviced from vhost worker thread */
>  	struct llist_node list;
> +	/* Indicate this event is issued during the flush operaton */
> +	int during_flush;
>  };
>  
>  /*
> -- 
> 1.8.1.4