Re: [PATCH v6 2/2] tcm_vhost: Wait for pending requests in vhost_scsi_flush()

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On Sun, Apr 28, 2013 at 03:48:23PM +0800, Asias He wrote:
> On Sat, Apr 27, 2013 at 10:40:41PM +0300, Michael S. Tsirkin wrote:
> > On Sat, Apr 27, 2013 at 11:16:49AM +0800, Asias He wrote:
> > > Unlike tcm_vhost_evt requests, tcm_vhost_cmd requests are passed to the
> > > target core system, we can not make sure all the pending requests will
> > > be finished by flushing the virt queue.
> > > 
> > > In this patch, we do refcount for every tcm_vhost_cmd requests to make
> > > vhost_scsi_flush() wait for all the pending requests issued before the
> > > flush operation to be finished.
> > > 
> > > This is useful when we call vhost_scsi_clear_endpoint() to stop
> > > tcm_vhost. No new requests will be passed to target core system because
> > > we clear the endpoint by setting vs_tpg to NULL. And we wait for all the
> > > old requests. These guarantee no requests will be leaked and existing
> > > requests will be completed.
> > > 
> > > Signed-off-by: Asias He <asias@xxxxxxxxxx>
> > > ---
> > >  drivers/vhost/tcm_vhost.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++-
> > >  drivers/vhost/tcm_vhost.h |  3 ++
> > >  2 files changed, 92 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> > > index 99d3480..afb5308 100644
> > > --- a/drivers/vhost/tcm_vhost.c
> > > +++ b/drivers/vhost/tcm_vhost.c
> > > @@ -74,8 +74,19 @@ enum {
> > >  #define VHOST_SCSI_MAX_VQ	128
> > >  #define VHOST_SCSI_MAX_EVENT	128
> > >  
> > > +struct vhost_scsi_inflight {
> > > +	/* Wait for the flush operation to finish */
> > > +	struct completion comp;
> > > +	/* Refcount for the inflight reqs */
> > > +	struct kref kref;
> > > +};
> > > +
> > >  struct vhost_scsi_virtqueue {
> > >  	struct vhost_virtqueue vq;
> > > +	/* Track inflight reqs, protected by vq->mutex */
> > 
> > Actually, it's protected by dev mutex: you drop
> > vq mutex before flush.
> 
> It is protected by both dev mutex and vq mutex.
> 
> take vq mutex -> vhost_scsi_allocate_cmd -> tcm_vhost_get_inflight ->
> access inflights[] and inflight_idx.
> 
> The dev mutex guarantees only one flush operation is in progress.

That's what I am saying. but vq mutex does nothing for inflights,
it merely protects inflight_idx.

> > > +	struct vhost_scsi_inflight inflights[2];
> > > +	/* Indicate current inflight in use, protected by vq->mutex */
> > > +	int inflight_idx;
> > >  };
> > >  
> > 
> > I'd be happier with a dynamically allocated inflights,
> > and simply pass it in to vhost_scsi_flush.
> > I guess we can do this in a follow-up cleanup.
> 
> No way to 100% guarantee the allocation will success, even if using
> mempool. So we need to check allocation failure anyway.
> 
> With dynamic allocation, we can allocate inflight and check before we do
> anything in the vhost_scsi_flush calling chain. Now we have 4 places
> calling vhost_scsi_flush. We need to add error handing code everywhere.
> 
> 1) vhost_scsi_release
> 2) vhost_scsi_set_endpoint
> 3) vhost_scsi_clear_endpoint
> 4) vhost_scsi_set_features
> 
> IMO, The static one works better.

Error handling is a standard easily understandable thing.
A custom locking scheme - not at all. Even when we think it's right,
above we are still arguing how to properly document it.

> > >  struct vhost_scsi {
> > > @@ -111,6 +122,59 @@ static int iov_num_pages(struct iovec *iov)
> > >  	       ((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT;
> > >  }
> > >  
> > > +void tcm_vhost_done_inflight(struct kref *kref)
> > > +{
> > > +	struct vhost_scsi_inflight *inflight;
> > > +
> > > +	inflight = container_of(kref, struct vhost_scsi_inflight, kref);
> > > +	complete(&inflight->comp);
> > > +}
> > > +
> > > +static void tcm_vhost_init_inflight(struct vhost_scsi *vs,
> > > +				    struct vhost_scsi_inflight *old_inflight[])
> > > +{
> > > +	struct vhost_scsi_inflight *new_inflight;
> > > +	struct vhost_virtqueue *vq;
> > > +	int idx, i;
> > > +
> > > +	for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
> > > +		vq = &vs->vqs[i].vq;
> > > +
> > > +		mutex_lock(&vq->mutex);
> > > +
> > > +		/* store old infight */
> > > +		idx = vs->vqs[i].inflight_idx;
> > > +		if (old_inflight)
> > > +			old_inflight[i] = &vs->vqs[i].inflights[idx];
> > > +
> > > +		/* setup new infight */
> > > +		vs->vqs[i].inflight_idx = idx ^ 1;
> > > +		new_inflight = &vs->vqs[i].inflights[idx ^ 1];
> > > +		kref_init(&new_inflight->kref);
> > > +		init_completion(&new_inflight->comp);
> > > +
> > > +		mutex_unlock(&vq->mutex);
> > > +	}
> > > +}
> > > +
> > > +static struct vhost_scsi_inflight *
> > > +tcm_vhost_get_inflight(struct vhost_virtqueue *vq)
> > > +{
> > > +	struct vhost_scsi_inflight *inflight;
> > > +	struct vhost_scsi_virtqueue *svq;
> > > +
> > > +	svq = container_of(vq, struct vhost_scsi_virtqueue, vq);
> > > +	inflight = &svq->inflights[svq->inflight_idx];
> > > +	kref_get(&inflight->kref);
> > > +
> > > +	return inflight;
> > > +}
> > > +
> > > +static void tcm_vhost_put_inflight(struct vhost_scsi_inflight *inflight)
> > > +{
> > > +	kref_put(&inflight->kref, tcm_vhost_done_inflight);
> > > +}
> > > +
> > >  static int tcm_vhost_check_true(struct se_portal_group *se_tpg)
> > >  {
> > >  	return 1;
> > > @@ -407,6 +471,8 @@ static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
> > >  		kfree(tv_cmd->tvc_sgl);
> > >  	}
> > >  
> > > +	tcm_vhost_put_inflight(tv_cmd->inflight);
> > > +
> > >  	kfree(tv_cmd);
> > >  }
> > >  
> > > @@ -533,6 +599,7 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
> > >  }
> > >  
> > >  static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
> > > +	struct vhost_virtqueue *vq,
> > >  	struct tcm_vhost_tpg *tv_tpg,
> > >  	struct virtio_scsi_cmd_req *v_req,
> > >  	u32 exp_data_len,
> > > @@ -557,6 +624,7 @@ 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->inflight = tcm_vhost_get_inflight(vq);
> > >  
> > >  	return tv_cmd;
> > >  }
> > > @@ -812,7 +880,7 @@ 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(vq, tv_tpg, &v_req,
> > >  					exp_data_len, data_direction);
> > >  		if (IS_ERR(tv_cmd)) {
> > >  			vq_err(vq, "vhost_scsi_allocate_cmd failed %ld\n",
> > > @@ -949,12 +1017,29 @@ static void vhost_scsi_flush_vq(struct vhost_scsi *vs, int index)
> > >  
> > >  static void vhost_scsi_flush(struct vhost_scsi *vs)
> > >  {
> > > +	struct vhost_scsi_inflight *old_inflight[VHOST_SCSI_MAX_VQ];
> > >  	int i;
> > >  
> > > +	/* Init new inflight and remember the old inflight */
> > > +	tcm_vhost_init_inflight(vs, old_inflight);
> > > +
> > > +	/*
> > > +	 * The inflight->kref was initialized to 1. We decrement it here to
> > > +	 * indicate the start of the flush operation so that it will reach 0
> > > +	 * when all the reqs are finished.
> > > +	 */
> > > +	for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
> > > +		kref_put(&old_inflight[i]->kref, tcm_vhost_done_inflight);
> > > +
> > > +	/* Flush both the vhost poll and vhost work */
> > >  	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 for all reqs issued before the flush to be finished */
> > > +	for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
> > > +		wait_for_completion(&old_inflight[i]->comp);
> > >  }
> > >  
> > >  /*
> > > @@ -1185,6 +1270,9 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
> > >  		s->vqs[i].vq.handle_kick = vhost_scsi_handle_kick;
> > >  	}
> > >  	r = vhost_dev_init(&s->dev, vqs, VHOST_SCSI_MAX_VQ);
> > > +
> > > +	tcm_vhost_init_inflight(s, NULL);
> > > +
> > >  	if (r < 0) {
> > >  		kfree(vqs);
> > >  		kfree(s);
> > > diff --git a/drivers/vhost/tcm_vhost.h b/drivers/vhost/tcm_vhost.h
> > > index 514b9fd..26a57c2 100644
> > > --- a/drivers/vhost/tcm_vhost.h
> > > +++ b/drivers/vhost/tcm_vhost.h
> > > @@ -2,6 +2,7 @@
> > >  #define TCM_VHOST_NAMELEN 256
> > >  #define TCM_VHOST_MAX_CDB_SIZE 32
> > >  
> > > +struct vhost_scsi_inflight;
> > >  struct tcm_vhost_cmd {
> > >  	/* Descriptor from vhost_get_vq_desc() for virt_queue segment */
> > >  	int tvc_vq_desc;
> > > @@ -37,6 +38,8 @@ 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;
> > > +	/* Used to track inflight cmd */
> > > +	struct vhost_scsi_inflight *inflight;
> > >  };
> > >  
> > >  struct tcm_vhost_nexus {
> > > -- 
> > > 1.8.1.4
> 
> -- 
> Asias
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