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 only lock if it is accessed in
the vhost worker thread, because it is protected by "vhost rcu".
Signed-off-by: Asias He <as...@redhat.com>
---
drivers/vhost/tcm_vhost.c | 38 +++++++++++++++++++++++++++++++++-----
1 file changed, 33 insertions(+), 5 deletions(-)
diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
index 5e3d4487..0524267 100644
--- a/drivers/vhost/tcm_vhost.c
+++ b/drivers/vhost/tcm_vhost.c
@@ -67,7 +67,6 @@ struct vhost_scsi {
/* Protected by vhost_scsi->dev.mutex */
struct tcm_vhost_tpg *vs_tpg[VHOST_SCSI_MAX_TARGET];
char vs_vhost_wwpn[TRANSPORT_IQN_LEN];
- bool vs_endpoint;
struct vhost_dev dev;
struct vhost_virtqueue vqs[VHOST_SCSI_MAX_VQ];
@@ -91,6 +90,24 @@ static int iov_num_pages(struct iovec *iov)
((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT;
}
+static bool tcm_vhost_check_endpoint(struct vhost_virtqueue *vq)
+{
+ bool ret = false;
+
+ /*
+ * 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
+ */
+ if (rcu_dereference_check(vq->private_data, 1))
+ ret = true;
+
+ return ret;
+}
+
static int tcm_vhost_check_true(struct se_portal_group *se_tpg)
{
return 1;
@@ -581,8 +598,7 @@ 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))
+ if (!tcm_vhost_check_endpoint(vq))
return;
mutex_lock(&vq->mutex);
@@ -829,11 +845,12 @@ static int vhost_scsi_set_endpoint(
sizeof(vs->vs_vhost_wwpn));
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);
vhost_init_used(vq);
mutex_unlock(&vq->mutex);
}
- vs->vs_endpoint = true;
ret = 0;
} else {
ret = -EEXIST;
@@ -849,6 +866,8 @@ 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;
@@ -884,9 +903,18 @@ 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);
+ }
+ }
mutex_unlock(&vs->dev.mutex);
return 0;
--
1.8.1.4
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