On Wed, Apr 03, 2013 at 02:17:37PM +0800, Asias He wrote:
> Currently, vs->vs_endpoint is used indicate if the endpoint is setup or
> not. It is set or cleared in vhost_scsi_set_endpoint() or
> vhost_scsi_clear_endpoint() under the vs->dev.mutex lock. However, when
> we check it in vhost_scsi_handle_vq(), we ignored the lock.
>
> Instead of using the vs->vs_endpoint and the vs->dev.mutex lock to
> indicate the status of the endpoint, we use per virtqueue
> vq->private_data to indicate it. In this way, we can only take the
> vq->mutex lock which is per queue and make the concurrent multiqueue
> process having less lock contention. Further, in the read side of
> vq->private_data, we can even do not take the lock if it is accessed in
> the vhost worker thread, because it is protected by "vhost rcu".
>
> Signed-off-by: Asias He <asias@xxxxxxxxxx>
Not strictly 3.9 material itself but needed for the next one.
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/vhost/tcm_vhost.c | 144 ++++++++++++++++++++++++++++++++--------------
> 1 file changed, 101 insertions(+), 43 deletions(-)
>
> diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> index 61f9eab..11121ea 100644
> --- a/drivers/vhost/tcm_vhost.c
> +++ b/drivers/vhost/tcm_vhost.c
> @@ -65,9 +65,8 @@ enum {
>
> struct vhost_scsi {
> /* Protected by vhost_scsi->dev.mutex */
> - struct tcm_vhost_tpg *vs_tpg[VHOST_SCSI_MAX_TARGET];
> + struct tcm_vhost_tpg **vs_tpg;
> char vs_vhost_wwpn[TRANSPORT_IQN_LEN];
> - bool vs_endpoint;
>
> struct vhost_dev dev;
> struct vhost_virtqueue vqs[VHOST_SCSI_MAX_VQ];
> @@ -573,6 +572,7 @@ static void tcm_vhost_submission_work(struct work_struct *work)
> static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
> struct vhost_virtqueue *vq)
> {
> + struct tcm_vhost_tpg **vs_tpg;
> struct virtio_scsi_cmd_req v_req;
> struct tcm_vhost_tpg *tv_tpg;
> struct tcm_vhost_cmd *tv_cmd;
> @@ -581,8 +581,16 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
> int head, ret;
> u8 target;
>
> - /* Must use ioctl VHOST_SCSI_SET_ENDPOINT */
> - if (unlikely(!vs->vs_endpoint))
> + /*
> + * We can handle the vq only after the endpoint is setup by calling the
> + * VHOST_SCSI_SET_ENDPOINT ioctl.
> + *
> + * TODO: Check that we are running from vhost_worker which acts
> + * as read-side critical section for vhost kind of RCU.
> + * See the comments in struct vhost_virtqueue in drivers/vhost/vhost.h
> + */
> + vs_tpg = rcu_dereference_check(vq->private_data, 1);
> + if (!vs_tpg)
> return;
>
> mutex_lock(&vq->mutex);
> @@ -652,7 +660,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
>
> /* Extract the tpgt */
> target = v_req.lun[1];
> - tv_tpg = ACCESS_ONCE(vs->vs_tpg[target]);
> + tv_tpg = ACCESS_ONCE(vs_tpg[target]);
>
> /* Target does not exist, fail the request */
> if (unlikely(!tv_tpg)) {
> @@ -771,6 +779,20 @@ static void vhost_scsi_handle_kick(struct vhost_work *work)
> vhost_scsi_handle_vq(vs, vq);
> }
>
> +static void vhost_scsi_flush_vq(struct vhost_scsi *vs, int index)
> +{
> + vhost_poll_flush(&vs->dev.vqs[index].poll);
> +}
> +
> +static void vhost_scsi_flush(struct vhost_scsi *vs)
> +{
> + int i;
> +
> + for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
> + vhost_scsi_flush_vq(vs, i);
> + vhost_work_flush(&vs->dev, &vs->vs_completion_work);
> +}
> +
> /*
> * Called from vhost_scsi_ioctl() context to walk the list of available
> * tcm_vhost_tpg with an active struct tcm_vhost_nexus
> @@ -781,8 +803,10 @@ static int vhost_scsi_set_endpoint(
> {
> struct tcm_vhost_tport *tv_tport;
> struct tcm_vhost_tpg *tv_tpg;
> + struct tcm_vhost_tpg **vs_tpg;
> + struct vhost_virtqueue *vq;
> + int index, ret, i, len;
> bool match = false;
> - int index, ret;
>
> mutex_lock(&vs->dev.mutex);
> /* Verify that ring has been setup correctly. */
> @@ -794,6 +818,15 @@ static int vhost_scsi_set_endpoint(
> }
> }
>
> + len = sizeof(vs_tpg[0]) * VHOST_SCSI_MAX_TARGET;
> + vs_tpg = kzalloc(len, GFP_KERNEL);
> + if (!vs_tpg) {
> + mutex_unlock(&vs->dev.mutex);
> + return -ENOMEM;
> + }
> + if (vs->vs_tpg)
> + memcpy(vs_tpg, vs->vs_tpg, len);
> +
> mutex_lock(&tcm_vhost_mutex);
> list_for_each_entry(tv_tpg, &tcm_vhost_list, tv_tpg_list) {
> mutex_lock(&tv_tpg->tv_tpg_mutex);
> @@ -808,14 +841,15 @@ static int vhost_scsi_set_endpoint(
> tv_tport = tv_tpg->tport;
>
> if (!strcmp(tv_tport->tport_name, t->vhost_wwpn)) {
> - if (vs->vs_tpg[tv_tpg->tport_tpgt]) {
> + if (vs->vs_tpg && vs->vs_tpg[tv_tpg->tport_tpgt]) {
> mutex_unlock(&tv_tpg->tv_tpg_mutex);
> mutex_unlock(&tcm_vhost_mutex);
> mutex_unlock(&vs->dev.mutex);
> + kfree(vs_tpg);
> return -EEXIST;
> }
> tv_tpg->tv_tpg_vhost_count++;
> - vs->vs_tpg[tv_tpg->tport_tpgt] = tv_tpg;
> + vs_tpg[tv_tpg->tport_tpgt] = tv_tpg;
> smp_mb__after_atomic_inc();
> match = true;
> }
> @@ -826,12 +860,26 @@ static int vhost_scsi_set_endpoint(
> if (match) {
> memcpy(vs->vs_vhost_wwpn, t->vhost_wwpn,
> sizeof(vs->vs_vhost_wwpn));
> - vs->vs_endpoint = true;
> + for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
> + vq = &vs->vqs[i];
> + /* Flushing the vhost_work acts as synchronize_rcu */
> + mutex_lock(&vq->mutex);
> + rcu_assign_pointer(vq->private_data, vs_tpg);
> + mutex_unlock(&vq->mutex);
> + }
> ret = 0;
> } else {
> ret = -EEXIST;
> }
>
> + /*
> + * Act as synchronize_rcu to make sure access to
> + * old vs->vs_tpg is finished.
> + */
> + vhost_scsi_flush(vs);
> + kfree(vs->vs_tpg);
> + vs->vs_tpg = vs_tpg;
> +
> mutex_unlock(&vs->dev.mutex);
> return ret;
> }
> @@ -842,6 +890,8 @@ static int vhost_scsi_clear_endpoint(
> {
> struct tcm_vhost_tport *tv_tport;
> struct tcm_vhost_tpg *tv_tpg;
> + struct vhost_virtqueue *vq;
> + bool match = false;
> int index, ret, i;
> u8 target;
>
> @@ -853,9 +903,14 @@ static int vhost_scsi_clear_endpoint(
> goto err_dev;
> }
> }
> +
> + if (!vs->vs_tpg) {
> + mutex_unlock(&vs->dev.mutex);
> + return 0;
> + }
> +
> for (i = 0; i < VHOST_SCSI_MAX_TARGET; i++) {
> target = i;
> -
> tv_tpg = vs->vs_tpg[target];
> if (!tv_tpg)
> continue;
> @@ -877,10 +932,27 @@ static int vhost_scsi_clear_endpoint(
> }
> tv_tpg->tv_tpg_vhost_count--;
> vs->vs_tpg[target] = NULL;
> - vs->vs_endpoint = false;
> + match = true;
> mutex_unlock(&tv_tpg->tv_tpg_mutex);
> }
> + if (match) {
> + for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
> + vq = &vs->vqs[i];
> + /* Flushing the vhost_work acts as synchronize_rcu */
> + mutex_lock(&vq->mutex);
> + rcu_assign_pointer(vq->private_data, NULL);
> + mutex_unlock(&vq->mutex);
> + }
> + }
> + /*
> + * Act as synchronize_rcu to make sure access to
> + * old vs->vs_tpg is finished.
> + */
> + vhost_scsi_flush(vs);
> + kfree(vs->vs_tpg);
> + vs->vs_tpg = NULL;
> mutex_unlock(&vs->dev.mutex);
> +
> return 0;
>
> err_tpg:
> @@ -890,6 +962,24 @@ err_dev:
> return ret;
> }
>
> +static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
> +{
> + if (features & ~VHOST_FEATURES)
> + return -EOPNOTSUPP;
> +
> + mutex_lock(&vs->dev.mutex);
> + if ((features & (1 << VHOST_F_LOG_ALL)) &&
> + !vhost_log_access_ok(&vs->dev)) {
> + mutex_unlock(&vs->dev.mutex);
> + return -EFAULT;
> + }
> + vs->dev.acked_features = features;
> + smp_wmb();
> + vhost_scsi_flush(vs);
> + mutex_unlock(&vs->dev.mutex);
> + return 0;
> +}
> +
> static int vhost_scsi_open(struct inode *inode, struct file *f)
> {
> struct vhost_scsi *s;
> @@ -930,38 +1020,6 @@ static int vhost_scsi_release(struct inode *inode, struct file *f)
> return 0;
> }
>
> -static void vhost_scsi_flush_vq(struct vhost_scsi *vs, int index)
> -{
> - vhost_poll_flush(&vs->dev.vqs[index].poll);
> -}
> -
> -static void vhost_scsi_flush(struct vhost_scsi *vs)
> -{
> - int i;
> -
> - for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
> - vhost_scsi_flush_vq(vs, i);
> - vhost_work_flush(&vs->dev, &vs->vs_completion_work);
> -}
> -
> -static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
> -{
> - if (features & ~VHOST_FEATURES)
> - return -EOPNOTSUPP;
> -
> - mutex_lock(&vs->dev.mutex);
> - if ((features & (1 << VHOST_F_LOG_ALL)) &&
> - !vhost_log_access_ok(&vs->dev)) {
> - mutex_unlock(&vs->dev.mutex);
> - return -EFAULT;
> - }
> - vs->dev.acked_features = features;
> - smp_wmb();
> - vhost_scsi_flush(vs);
> - mutex_unlock(&vs->dev.mutex);
> - return 0;
> -}
> -
> static long vhost_scsi_ioctl(struct file *f, unsigned int ioctl,
> unsigned long arg)
> {
> --
> 1.8.1.4
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