tcm_vhost: Use llist for cmd completion list

This drops the cmd completion list spin lock and makes the cmd
completion queue lock-less.

Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 13 insertions, 33 deletions

diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
index 22321cf84fbe..77d760bb2e44 100644
--- a/drivers/vhost/tcm_vhost.c
+++ b/drivers/vhost/tcm_vhost.c
@@ -47,6 +47,7 @@
 #include <linux/vhost.h>
 #include <linux/virtio_net.h> /* TODO vhost.h currently depends on this */
 #include <linux/virtio_scsi.h>
+#include <linux/llist.h>
 
 #include "vhost.c"
 #include "vhost.h"
@@ -64,8 +65,7 @@ struct vhost_scsi {
         struct vhost_virtqueue vqs[3];
 
         struct vhost_work vs_completion_work; /* cmd completion work item */
-        struct list_head vs_completion_list;  /* cmd completion queue */
-        spinlock_t vs_completion_lock;        /* protects s_completion_list */
+        struct llist_head vs_completion_list; /* cmd completion queue */
 };
 
 /* Local pointer to allocated TCM configfs fabric module */
@@ -301,9 +301,7 @@ static void vhost_scsi_complete_cmd(struct tcm_vhost_cmd *tv_cmd)
 {
         struct vhost_scsi *vs = tv_cmd->tvc_vhost;
 
-        spin_lock_bh(&vs->vs_completion_lock);
-        list_add_tail(&tv_cmd->tvc_completion_list, &vs->vs_completion_list);
-        spin_unlock_bh(&vs->vs_completion_lock);
+        llist_add(&tv_cmd->tvc_completion_list, &vs->vs_completion_list);
 
         vhost_work_queue(&vs->dev, &vs->vs_completion_work);
 }
@@ -347,27 +345,6 @@ static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
         kfree(tv_cmd);
 }
 
-/* Dequeue a command from the completion list */
-static struct tcm_vhost_cmd *vhost_scsi_get_cmd_from_completion(
-        struct vhost_scsi *vs)
-{
-        struct tcm_vhost_cmd *tv_cmd = NULL;
-
-        spin_lock_bh(&vs->vs_completion_lock);
-        if (list_empty(&vs->vs_completion_list)) {
-                spin_unlock_bh(&vs->vs_completion_lock);
-                return NULL;
-        }
-
-        list_for_each_entry(tv_cmd, &vs->vs_completion_list,
-                            tvc_completion_list) {
-                list_del(&tv_cmd->tvc_completion_list);
-                break;
-        }
-        spin_unlock_bh(&vs->vs_completion_lock);
-        return tv_cmd;
-}
-
 /* 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
@@ -377,12 +354,18 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
 {
         struct vhost_scsi *vs = container_of(work, struct vhost_scsi,
                                         vs_completion_work);
+        struct virtio_scsi_cmd_resp v_rsp;
         struct tcm_vhost_cmd *tv_cmd;
+        struct llist_node *llnode;
+        struct se_cmd *se_cmd;
+        int ret;
 
-        while ((tv_cmd = vhost_scsi_get_cmd_from_completion(vs))) {
-                struct virtio_scsi_cmd_resp v_rsp;
-                struct se_cmd *se_cmd = &tv_cmd->tvc_se_cmd;
-                int ret;
+        llnode = llist_del_all(&vs->vs_completion_list);
+        while (llnode) {
+                tv_cmd = llist_entry(llnode, struct tcm_vhost_cmd,
+                                     tvc_completion_list);
+                llnode = llist_next(llnode);
+                se_cmd = &tv_cmd->tvc_se_cmd;
 
                 pr_debug("%s tv_cmd %p resid %u status %#02x\n", __func__,
                         tv_cmd, se_cmd->residual_count, se_cmd->scsi_status);
@@ -426,7 +409,6 @@ static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
                 pr_err("Unable to allocate struct tcm_vhost_cmd\n");
                 return ERR_PTR(-ENOMEM);
         }
-        INIT_LIST_HEAD(&tv_cmd->tvc_completion_list);
         tv_cmd->tvc_tag = v_req->tag;
         tv_cmd->tvc_task_attr = v_req->task_attr;
         tv_cmd->tvc_exp_data_len = exp_data_len;
@@ -857,8 +839,6 @@ 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);
-        INIT_LIST_HEAD(&s->vs_completion_list);
-        spin_lock_init(&s->vs_completion_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;