The commit is pushed to "branch-rh9-5.14.0-70.22.1.vz9.17.x-ovz" and will 
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh9-5.14.0-70.22.1.vz9.17.9
------>
commit 71a06fa299a0ee1272e4e4ecd94dd5535f7eaee6
Author: Konstantin Khorenko <khore...@virtuozzo.com>
Date:   Wed Nov 16 15:56:19 2022 +0300

    Revert "drivers/vhost: use array to store workers"
    
    This reverts commit 10a96129bac144bbbc433b9738cd144ae0265d9a.
    
    Will apply v5 of the patchset.
    https://jira.sw.ru/browse/PSBM-139414
    
    Signed-off-by: Konstantin Khorenko <khore...@virtuozzo.com>
---
 drivers/vhost/vhost.c | 75 +++++++++++++++------------------------------------
 drivers/vhost/vhost.h | 10 +------
 2 files changed, 22 insertions(+), 63 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 968601325a37..a0bfc77c6a43 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -231,24 +231,11 @@ void vhost_poll_stop(struct vhost_poll *poll)
 }
 EXPORT_SYMBOL_GPL(vhost_poll_stop);
 
-static void vhost_work_queue_at_worker(struct vhost_worker *w,
-                                      struct vhost_work *work)
-{
-       if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
-               /* We can only add the work to the list after we're
-                * sure it was not in the list.
-                * test_and_set_bit() implies a memory barrier.
-                */
-               llist_add(&work->node, &w->work_list);
-               wake_up_process(w->worker);
-       }
-}
-
 void vhost_work_dev_flush(struct vhost_dev *dev)
 {
        struct vhost_flush_struct flush;
 
-       if (dev->workers[0].worker) {
+       if (dev->worker) {
                init_completion(&flush.wait_event);
                vhost_work_init(&flush.work, vhost_flush_work);
 
@@ -268,12 +255,17 @@ EXPORT_SYMBOL_GPL(vhost_poll_flush);
 
 void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
 {
-       struct vhost_worker *w = &dev->workers[0];
-
-       if (!w->worker)
+       if (!dev->worker)
                return;
 
-       vhost_work_queue_at_worker(w, work);
+       if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
+               /* We can only add the work to the list after we're
+                * sure it was not in the list.
+                * test_and_set_bit() implies a memory barrier.
+                */
+               llist_add(&work->node, &dev->work_list);
+               wake_up_process(dev->worker);
+       }
 }
 EXPORT_SYMBOL_GPL(vhost_work_queue);
 
@@ -349,29 +341,9 @@ static void vhost_vq_reset(struct vhost_dev *dev,
        __vhost_vq_meta_reset(vq);
 }
 
-static void vhost_worker_reset(struct vhost_worker *w)
-{
-       init_llist_head(&w->work_list);
-       w->worker = NULL;
-}
-
-void vhost_cleanup_workers(struct vhost_dev *dev)
-{
-       int i;
-
-       for (i = 0; i < dev->nworkers; ++i) {
-               WARN_ON(!llist_empty(&dev->workers[i].work_list));
-               kthread_stop(dev->workers[i].worker);
-               vhost_worker_reset(&dev->workers[i]);
-       }
-
-       dev->nworkers = 0;
-}
-
 static int vhost_worker(void *data)
 {
-       struct vhost_worker *w = data;
-       struct vhost_dev *dev = w->dev;
+       struct vhost_dev *dev = data;
        struct vhost_work *work, *work_next;
        struct llist_node *node;
 
@@ -386,7 +358,7 @@ static int vhost_worker(void *data)
                        break;
                }
 
-               node = llist_del_all(&w->work_list);
+               node = llist_del_all(&dev->work_list);
                if (!node)
                        schedule();
 
@@ -509,6 +481,7 @@ void vhost_dev_init(struct vhost_dev *dev,
        dev->umem = NULL;
        dev->iotlb = NULL;
        dev->mm = NULL;
+       dev->worker = NULL;
        dev->iov_limit = iov_limit;
        dev->weight = weight;
        dev->byte_weight = byte_weight;
@@ -520,11 +493,6 @@ void vhost_dev_init(struct vhost_dev *dev,
        INIT_LIST_HEAD(&dev->pending_list);
        spin_lock_init(&dev->iotlb_lock);
 
-       dev->nworkers = 0;
-       for (i = 0; i < VHOST_MAX_WORKERS; ++i) {
-               dev->workers[i].dev = dev;
-               vhost_worker_reset(&dev->workers[i]);
-       }
 
        for (i = 0; i < dev->nvqs; ++i) {
                vq = dev->vqs[i];
@@ -634,8 +602,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
                        goto err_worker;
                }
 
-               dev->workers[0].worker = worker;
-               dev->nworkers = 1;
+               dev->worker = worker;
                wake_up_process(worker); /* avoid contributing to loadavg */
 
                err = vhost_attach_cgroups(dev);
@@ -649,10 +616,9 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
 
        return 0;
 err_cgroup:
-       dev->nworkers = 0;
-       if (dev->workers[0].worker) {
-               kthread_stop(dev->workers[0].worker);
-               dev->workers[0].worker = NULL;
+       if (dev->worker) {
+               kthread_stop(dev->worker);
+               dev->worker = NULL;
        }
 err_worker:
        vhost_detach_mm(dev);
@@ -735,7 +701,6 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
                        eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx);
                vhost_vq_reset(dev, dev->vqs[i]);
        }
-
        vhost_dev_free_iovecs(dev);
        if (dev->log_ctx)
                eventfd_ctx_put(dev->log_ctx);
@@ -747,8 +712,10 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
        dev->iotlb = NULL;
        vhost_clear_msg(dev);
        wake_up_interruptible_poll(&dev->wait, EPOLLIN | EPOLLRDNORM);
-       if (dev->use_worker) {
-               vhost_cleanup_workers(dev);
+       WARN_ON(!llist_empty(&dev->work_list));
+       if (dev->worker) {
+               kthread_stop(dev->worker);
+               dev->worker = NULL;
                dev->kcov_handle = 0;
        }
        vhost_detach_mm(dev);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 634ea828cbba..638bb640d6b4 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -25,13 +25,6 @@ struct vhost_work {
        unsigned long           flags;
 };
 
-#define VHOST_MAX_WORKERS 4
-struct vhost_worker {
-       struct task_struct *worker;
-       struct llist_head work_list;
-       struct vhost_dev *dev;
-};
-
 /* Poll a file (eventfd or socket) */
 /* Note: there's nothing vhost specific about this structure. */
 struct vhost_poll {
@@ -156,8 +149,7 @@ struct vhost_dev {
        int nvqs;
        struct eventfd_ctx *log_ctx;
        struct llist_head work_list;
-       struct vhost_worker workers[VHOST_MAX_WORKERS];
-       int nworkers;
+       struct task_struct *worker;
        struct vhost_iotlb *umem;
        struct vhost_iotlb *iotlb;
        spinlock_t iotlb_lock;
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