On Sun, Apr 14, 2013 at 12:58:03PM +0300, Michael S. Tsirkin wrote:
> On Sat, Apr 13, 2013 at 11:29:14AM +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 v4:
> > - Introduce vhost_scsi_inflight
> > - Drop array to track flush
> > - Use RCU to protect vs_inflight explicitly
> >
> > 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@xxxxxxxxxx>
> > ---
> > drivers/vhost/tcm_vhost.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++
> > drivers/vhost/tcm_vhost.h | 5 ++++
> > 2 files changed, 78 insertions(+)
> >
> > diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> > index e09f0fe..5dde525 100644
> > --- a/drivers/vhost/tcm_vhost.c
> > +++ b/drivers/vhost/tcm_vhost.c
> > @@ -74,6 +74,11 @@ enum {
> > #define VHOST_SCSI_MAX_VQ 128
> > #define VHOST_SCSI_MAX_EVENT 128
> >
> > +struct vhost_scsi_inflight {
> > + wait_queue_head_t wait;
> > + atomic_t count;
>
> Okay now let's switch to kref + completion, make it more
> descriptive.
I still do not see why kref is better. Completion sounds good.
> > +};
> > +
> > struct vhost_scsi {
> > /* Protected by vhost_scsi->dev.mutex */
> > struct tcm_vhost_tpg **vs_tpg;
> > @@ -91,6 +96,8 @@ 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 */
> > +
> > + struct vhost_scsi_inflight __rcu *vs_inflight; /* track inflight req */
> > };
> >
> > /* Local pointer to allocated TCM configfs fabric module */
> > @@ -108,6 +115,51 @@ static int iov_num_pages(struct iovec *iov)
> > ((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT;
> > }
> >
> > +static struct vhost_scsi_inflight *
> > +tcm_vhost_alloc_inflight(struct vhost_scsi *vs)
> > +{
> > + struct vhost_scsi_inflight *inflight;
> > +
> > + inflight = kzalloc(sizeof(*inflight), GFP_KERNEL);
> > + if (inflight) {
>
> This is used in set_features, so let's make it int
> and return error to user if not. No need to corrupt kernel
> memory silently like this.
What do you mean by used in set_features? The return value of
tcm_vhost_alloc_inflight was used at some point, but now it is not used.
So I will return int.
Why is it corrupted?
>
>
> > + atomic_set(&inflight->count, 0);
>
>
> Ugh. So once all requests finish, refcount is 0
> and then inflight is freed, and then the next request will
> get a freed inflight value and dereference. Looks pretty bad,
> but maybe there's an increment somewhere that fixes it.
How can the next request get a freed inflight? It can not happen. The
old inflight is freed only after all the requests which reference it are
finished. See the last few lines in vhost_scsi_flush.
> But let's not go there. That's why I said above we should use kref +
> completion. That makes is very clear how to use it correctly.
> So:
> - initialize to 1
> - swap pointer with RCU
> - decrement
> - wait_for_completion
We can not go there.
>
>
> > + init_waitqueue_head(&inflight->wait);
> > + }
> > + rcu_assign_pointer(vs->vs_inflight, inflight);
> > + synchronize_rcu();
> > +
> > + return inflight;
> > +}
> > +
>
> This looks like it will overwrite inflight without
> freeing the old one. In fact it won't because caller
> has saved the pointer but this interface is
> just too tricky. Please just opencode this function.
>
Did you see the old inflight was freed in vhost_scsi_flush().
It was code in a helper function because it is used in too places.
One is in vhost_scsi_open and the other is in vhost_scsi_scsi?
>
> > +static struct vhost_scsi_inflight *
> > +tcm_vhost_inc_inflight(struct vhost_scsi *vs)
> > +{
> > + struct vhost_scsi_inflight *inflight;
> > +
> > + rcu_read_lock();
> > + inflight = rcu_dereference(vs->vs_inflight);
> > + if (inflight)
>
> How can it be NULL?
When tcm_vhost_alloc_inflight failed to allocate inflight.
> > + atomic_inc(&inflight->count);
> > + rcu_read_unlock();
> > +
> > + return inflight;
> > +}
> > +
> > +static void tcm_vhost_dec_inflight(struct vhost_scsi_inflight *inflight)
> > +{
> > + /*
> > + * Wakeup the waiter when all the requests issued before the flush
> > + * operation are finished.
> > + */
> > + if (inflight && !atomic_dec_return(&inflight->count))
> > + wake_up(&inflight->wait);
> > +}
> > +
> > +static bool tcm_vhost_done_inflight(struct vhost_scsi_inflight *inflight)
> > +{
> > + return atomic_read(&inflight->count) == 0;
> > +}
> > +
> > static bool tcm_vhost_check_feature(struct vhost_scsi *vs, int feature)
> > {
> > bool ret = false;
> > @@ -402,6 +454,7 @@ 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(evt->inflight);
> > vs->vs_events_nr--;
> > kfree(evt);
> > mutex_unlock(&vs->vs_events_lock);
> > @@ -423,6 +476,7 @@ static struct tcm_vhost_evt *tcm_vhost_allocate_evt(struct vhost_scsi *vs,
> > if (evt) {
> > evt->event.event = event;
> > evt->event.reason = reason;
> > + evt->inflight = tcm_vhost_inc_inflight(vs);
> > vs->vs_events_nr++;
> > }
> > mutex_unlock(&vs->vs_events_lock);
> > @@ -445,6 +499,8 @@ static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
> > kfree(tv_cmd->tvc_sgl);
> > }
> >
> > + tcm_vhost_dec_inflight(tv_cmd->inflight);
> > +
> > kfree(tv_cmd);
> > }
> >
> > @@ -595,6 +651,7 @@ static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
> > tv_cmd->tvc_data_direction = data_direction;
> > tv_cmd->tvc_nexus = tv_nexus;
> > tv_cmd->tvc_vhost = vs;
> > + tv_cmd->inflight = tcm_vhost_inc_inflight(vs);
> >
> > return tv_cmd;
> > }
> > @@ -983,10 +1040,22 @@ static void vhost_scsi_flush_vq(struct vhost_scsi *vs, int index)
> > static void vhost_scsi_flush(struct vhost_scsi *vs)
> > {
> > int i;
> > + struct vhost_scsi_inflight *inflight;
> > +
> > + inflight = ACCESS_ONCE(vs->vs_inflight);
>
> rcu_dereference_protected ? This ACCESS_ONCE looks bogus.
okay.
> > + if (!tcm_vhost_alloc_inflight(vs))
> > + return;
> >
> > 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 */
>
> s/until/for/
okay.
> > + if (inflight) {
>
> How can this be NULL?
When tcm_vhost_alloc_inflight failed to allocate inflight.
> > + wait_event(inflight->wait, tcm_vhost_done_inflight(inflight));
> > + kfree(inflight);
> > + }
> > }
> >
> > /*
> > @@ -1195,6 +1264,9 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
> > s->vs_events_dropped = false;
> > mutex_init(&s->vs_events_lock);
> >
> > + if (!tcm_vhost_alloc_inflight(s))
> > + return -ENOMEM;
> > +
> > 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++)
> > @@ -1220,6 +1292,7 @@ static int vhost_scsi_release(struct inode *inode, struct file *f)
> > vhost_scsi_clear_endpoint(s, &t);
> > vhost_dev_stop(&s->dev);
> > vhost_dev_cleanup(&s->dev, false);
> > + kfree(s->vs_inflight);
> > kfree(s);
> > return 0;
> > }
> > diff --git a/drivers/vhost/tcm_vhost.h b/drivers/vhost/tcm_vhost.h
> > index 94e9ee53..7567767 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 req */
> > + struct vhost_scsi_inflight *inflight;
> > };
> >
> > struct tcm_vhost_nexus {
> > @@ -91,6 +94,8 @@ struct tcm_vhost_evt {
> > struct virtio_scsi_event event;
> > /* virtio_scsi event list, serviced from vhost worker thread */
> > struct llist_node list;
> > + /* Used to track inflight req */
> > + struct vhost_scsi_inflight *inflight;
> > };
> >
> > /*
> > --
> > 1.8.1.4
--
Asias
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