[PATCH 5/5] vhost-scsi: Reduce vhost_scsi_mutex use

[Mike Christie <michael.christie@oracle.com>]

Now that vhost_scsi_clear_endpoint will prevent new IO and flush running
IO before dropping it's refcounts on the tpg, we only need to hold the
vhost_scsi_mutex while looping over tpgs and taking a refcount, and when
manipulating the tpg list.

This removes the vhost_scsi_mutex from vhost_scsi_clear_endpoint and moves
the vhost_scsi_mutex use in vhost_scsi_set_endpoint so it's only taken
while looping over the tpgs and taking a refcount. We can then now avoid
issues where vhost_scsi_set_endpoint has to wait for another device's
vhost_scsi_clear_endpoint call.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
---
 drivers/vhost/scsi.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index c405ab5c232a..75ea24f1c571 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1540,7 +1540,7 @@ static int vhost_scsi_setup_vq_cmds(struct vhost_virtqueue *vq, int max_cmds)
  * vhost_scsi_tpg with an active struct vhost_scsi_nexus
  *
  *  The lock nesting rule is:
- *    vhost_scsi_mutex -> vs->dev.mutex -> tpg->tv_tpg_mutex -> vq->mutex
+ *    vs->dev.mutex -> vhost_scsi_mutex -> tpg->tv_tpg_mutex -> vq->mutex
  */
 static int
 vhost_scsi_set_endpoint(struct vhost_scsi *vs,
@@ -1554,7 +1554,6 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 	int index, ret, i, len;
 	bool match = false;
 
-	mutex_lock(&vhost_scsi_mutex);
 	mutex_lock(&vs->dev.mutex);
 
 	/* Verify that ring has been setup correctly. */
@@ -1575,6 +1574,7 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 	if (vs->vs_tpg)
 		memcpy(vs_tpg, vs->vs_tpg, len);
 
+	mutex_lock(&vhost_scsi_mutex);
 	list_for_each_entry(tpg, &vhost_scsi_list, tv_tpg_list) {
 		mutex_lock(&tpg->tv_tpg_mutex);
 		if (!tpg->tpg_nexus) {
@@ -1590,6 +1590,7 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 		if (!strcmp(tv_tport->tport_name, t->vhost_wwpn)) {
 			if (vs->vs_tpg && vs->vs_tpg[tpg->tport_tpgt]) {
 				mutex_unlock(&tpg->tv_tpg_mutex);
+				mutex_unlock(&vhost_scsi_mutex);
 				ret = -EEXIST;
 				goto undepend;
 			}
@@ -1604,6 +1605,7 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 			if (ret) {
 				pr_warn("target_depend_item() failed: %d\n", ret);
 				mutex_unlock(&tpg->tv_tpg_mutex);
+				mutex_unlock(&vhost_scsi_mutex);
 				goto undepend;
 			}
 			tpg->tv_tpg_vhost_count++;
@@ -1613,6 +1615,7 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 		}
 		mutex_unlock(&tpg->tv_tpg_mutex);
 	}
+	mutex_unlock(&vhost_scsi_mutex);
 
 	if (match) {
 		memcpy(vs->vs_vhost_wwpn, t->vhost_wwpn,
@@ -1667,7 +1670,6 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 	kfree(vs_tpg);
 out:
 	mutex_unlock(&vs->dev.mutex);
-	mutex_unlock(&vhost_scsi_mutex);
 	return ret;
 }
 
@@ -1683,7 +1685,6 @@ vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
 	int index, ret, i;
 	u8 target;
 
-	mutex_lock(&vhost_scsi_mutex);
 	mutex_lock(&vs->dev.mutex);
 	/* Verify that ring has been setup correctly. */
 	for (index = 0; index < vs->dev.nvqs; ++index) {
@@ -1765,12 +1766,10 @@ vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
 	vs->vs_tpg = NULL;
 	WARN_ON(vs->vs_events_nr);
 	mutex_unlock(&vs->dev.mutex);
-	mutex_unlock(&vhost_scsi_mutex);
 	return 0;
 
 err_dev:
 	mutex_unlock(&vs->dev.mutex);
-	mutex_unlock(&vhost_scsi_mutex);
 	return ret;
 }
 
-- 
2.25.1