On Thu, Apr 18, 2013 at 11:21:54AM +0300, Michael S. Tsirkin wrote:
> On Thu, Apr 18, 2013 at 04:59:08PM +0800, Asias He wrote:
> > On Thu, Apr 18, 2013 at 10:34:29AM +0300, Michael S. Tsirkin wrote:
> > > 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@xxxxxxxxxx>
> > > > Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> > > > ---
> > > > 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.
> > >
> >
> > Do you see a real problem?
>
> Complexity is a real problem. My head already spins. No I don't see a
> bug, but we need to simplify locking.
>
> And I think I see a nice way to do this:
> 1. move away from a global work to per-event work - so no list
> 2. remove dynamic allocation of events - so no events_nr
> 3. set/test overrun flag under the appropriate vq mutex
>
> I think that's ideal. But we can move there in small steps. As a first
> step - why can't we always take the vq mutex lock and drop
> vs_events_lock?
There are really different ways to solve the same problem. You are
welcome to implement you ideas.
> > > > + 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.
> >
> > Not really! evt->event.lun[4-7] is not initialized. It needs to be 0.
>
> So that is 4 bytes just init them when you set rest of lun.
It is not in the fast path. You can do it this way but not a must.
> > > 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?
> >
> > It is limited by VHOST_SCSI_MAX_EVENT.
>
> OK I missed that. But where does VHOST_SCSI_MAX_EVENT come from by the
> way? I don't see it in spec or did I miss it? It seems it's best not
> to lost events as long as there are descriptors in the event vq.
You wanted this.
> > >
> > > > + if (evt) {
> > >
> > > Let's do clean error handling here and above:
> > > if (!evt)
> > > goto err;
> >
> > We can you do in err? You simply unlock and return. Why bother? How
> > cleaner it will be.
>
> There's another error above and we'll share code.
> It's not a big issue, just a bit nicer IMHO.
Can't we focus on real issues other than this?
> > > > + 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.
> >
> > This makes extra indention which is more ugly.
>
> I don't care. No loops with goto and that's a hard rule.
It is not a loop.
> > > > + 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.
> >
> > Why it is simpler?
>
> simple list_ with a lock is easier to use correctly.
You need to use it correctly anyway for cmd. Why you want a lock here?
> > We are using llist for cmd. Why it is better using
> > one for evt and the different for cmd? Similar code makes people easier
> > to read.
>
> OK fair enough. But my idea is above to use a work
> structure instead of a list of events.
> This way we don't need extra list at all,
> no new locks, nothing.
Again, You are welcome to implement your ideas.
> > > > + 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.
> >
> > Why?
>
> Same as above.
> Because it's not safe to do this outside the vq mutex.
Is it also not safe to the same in -net? Why is it not safe?
> > > > +
> > > > + 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?
> >
> > When tpg->vhost_scsi has not been setup. E.g. no one starts a vhost-scsi
> > guest.
>
> So ENODEV or something.
okay.
> > > > +
> > > > + 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 ...
> >
> >
> > It make people easier to understand what's the true and false is about
> > in tcm_vhost_do_plug.
>
> So just pass in the reason and not a bool.
> When readers see
> VIRTIO_SCSI_EVT_RESET_RESCAN/VIRTIO_SCSI_EVT_RESET_REMOVED
> they will know what is going on.
How can you make the connection that VIRTIO_SCSI_EVT_RESET_RESCAN is
hotplug and VIRTIO_SCSI_EVT_RESET_REMOVED is hot-unplug at first glance?
> > > > 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
> >
> > --
> > Asias
--
Asias
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