Added back the previously removed function vhost_worker_queue() and
renamed it to vhost_worker_queue_khtread(). The new vhost_worker_queue()
will select the different mode based on the value of the parameter.

The old function vhost_work_queue()  was change to support task in
commit 6e890c5d5021 ('vhost: use vhost_tasks for worker threads')
changed in
commit f9010dbdc ('fork, vhost: Use CLONE_THREAD to fix freezer/ps regression')
and also was change the name of function to vhost_worker_queue() in
commit 0921dddcb5 (vhost: take worker or vq instead of dev for queueing)

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c | 30 ++++++++++++++++++++++++++++--
 drivers/vhost/vhost.h |  1 +
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index be43181af659..6198c165ab15 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -236,8 +236,8 @@ void vhost_poll_stop(struct vhost_poll *poll)
 }
 EXPORT_SYMBOL_GPL(vhost_poll_stop);
 
-static void vhost_worker_queue(struct vhost_worker *worker,
-			       struct vhost_work *work)
+static void vhost_worker_queue_task(struct vhost_worker *worker,
+				    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
@@ -249,6 +249,32 @@ static void vhost_worker_queue(struct vhost_worker *worker,
 	}
 }
 
+static void vhost_work_queue_kthread(struct vhost_worker *worker,
+				     struct vhost_work *work)
+{
+	if (!worker)
+		return;
+
+	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, &worker->work_list);
+
+		wake_up_process(worker->task);
+	}
+}
+
+static void vhost_worker_queue(struct vhost_worker *worker,
+			       struct vhost_work *work)
+{
+	if (use_kthread) {
+		vhost_work_queue_kthread(worker, work);
+	} else {
+		vhost_worker_queue_task(worker, work);
+	}
+}
 bool vhost_vq_work_queue(struct vhost_virtqueue *vq, struct vhost_work *work)
 {
 	struct vhost_worker *worker;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index bb75a292d50c..c7f126fd09e8 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -27,6 +27,7 @@ struct vhost_work {
 };
 
 struct vhost_worker {
+	struct task_struct	*task;
 	struct vhost_task	*vtsk;
 	struct vhost_dev	*dev;
 	/* Used to serialize device wide flushing with worker swapping. */
-- 
2.45.0

Hi Cindy,

kernel test robot noticed the following build errors:

[auto build test ERROR on mst-vhost/linux-next]
[also build test ERROR on linus/master v6.11-rc7 next-20240910]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Cindy-Lu/vhost-Add-a-new-module_param-for-enable-kthread/20240909-093852
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next
patch link:    https://lore.kernel.org/r/20240909013531.1243525-3-lulu%40redhat.com
patch subject: [PATCH v1 2/7] vhost: Add kthread support in function vhost_worker_queue()
config: arc-randconfig-001-20240911 (https://download.01.org/0day-ci/archive/20240911/202409111842.o3eEppU6-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240911/202409111842.o3eEppU6-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409111842.o3eEppU6-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/vhost/vhost.c: In function 'vhost_worker_queue':
>> drivers/vhost/vhost.c:272:13: error: 'use_kthread' undeclared (first use in this function)
     272 |         if (use_kthread) {
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c:272:13: note: each undeclared identifier is reported only once for each function it appears in


vim +/use_kthread +272 drivers/vhost/vhost.c

   268	
   269	static void vhost_worker_queue(struct vhost_worker *worker,
   270				       struct vhost_work *work)
   271	{
 > 272		if (use_kthread) {
   273			vhost_work_queue_kthread(worker, work);
   274		} else {
   275			vhost_worker_queue_task(worker, work);
   276		}
   277	}
   278	bool vhost_vq_work_queue(struct vhost_virtqueue *vq, struct vhost_work *work)
   279	{
   280		struct vhost_worker *worker;
   281		bool queued = false;
   282	
   283		rcu_read_lock();
   284		worker = rcu_dereference(vq->worker);
   285		if (worker) {
   286			queued = true;
   287			vhost_worker_queue(worker, work);
   288		}
   289		rcu_read_unlock();
   290	
   291		return queued;
   292	}
   293	EXPORT_SYMBOL_GPL(vhost_vq_work_queue);
   294	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki