Split the function vhost_worker_create to support both task and kthread
       
Added back the previous old function vhost_worker_create and rename it to
vhost_worker_create_khtread to support the khtread.

The new vhost_worker_create will be selected which to use based on the
value of the parameter.

the old function vhost_worker_create was change to support task in
commit 6e890c5d5021 ('vhost: use vhost_tasks for worker threads')
also changed in
commit 1cdaafa1b8b ('vhost: replace single worker pointer with xarray')
commit c011bb669dd ('vhost: dynamically allocate vhost_worker')

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c | 55 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 54 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index f05545b125f0..bf1e971cb06f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -807,7 +807,8 @@ static void vhost_workers_free(struct vhost_dev *dev)
 	else
 		vhost_workers_free_task(dev);
 }
-static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
+
+static struct vhost_worker *vhost_worker_create_task(struct vhost_dev *dev)
 {
 	struct vhost_worker *worker;
 	struct vhost_task *vtsk;
@@ -848,6 +849,50 @@ static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
 	return NULL;
 }
 
+static struct vhost_worker *vhost_worker_create_kthread(struct vhost_dev *dev)
+{
+	struct vhost_worker *worker;
+	struct task_struct *task;
+	int ret;
+	u32 id;
+
+	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
+	if (!worker)
+		return NULL;
+
+	worker->dev = dev;
+	worker->kcov_handle = kcov_common_handle();
+
+	mutex_init(&worker->mutex);
+	init_llist_head(&worker->work_list);
+
+	task = kthread_create(vhost_run_work_kthread_list, worker, "vhost-%d",
+			      current->pid);
+	if (IS_ERR(task)) {
+		ret = PTR_ERR(task);
+		goto free_worker;
+	}
+
+	worker->task = task;
+	wake_up_process(task); /* avoid contributing to loadavg */
+	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+	if (ret < 0)
+		goto stop_worker;
+	worker->id = id;
+
+	ret = vhost_attach_cgroups(dev);
+	if (ret)
+		goto stop_worker;
+
+	return worker;
+
+stop_worker:
+	kthread_stop(worker->task);
+free_worker:
+	kfree(worker);
+	return NULL;
+}
+
 /* Caller must have device mutex */
 static void __vhost_vq_attach_worker(struct vhost_virtqueue *vq,
 				     struct vhost_worker *worker)
@@ -936,6 +981,14 @@ static int vhost_vq_attach_worker(struct vhost_virtqueue *vq,
 	return 0;
 }
 
+static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
+{
+	if (use_kthread)
+		return vhost_worker_create_kthread(dev);
+	else
+		return vhost_worker_create_task(dev);
+}
+
 /* Caller must have device mutex */
 static int vhost_new_worker(struct vhost_dev *dev,
 			    struct vhost_worker_state *info)
-- 
2.45.0

Hi Cindy,

kernel test robot noticed the following build warnings:

[auto build test WARNING on mst-vhost/linux-next]
[also build test WARNING 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/20240909013531.1243525-7-lulu%40redhat.com
patch subject: [PATCH v1 6/7] vhost: Add kthread support in function vhost_worker_create
config: arc-randconfig-001-20240911 (https://download.01.org/0day-ci/archive/20240911/202409112050.3zbvpbyT-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/20240911/202409112050.3zbvpbyT-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/202409112050.3zbvpbyT-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/vhost/vhost.c: In function 'vhost_worker_queue':
   drivers/vhost/vhost.c:273:13: error: 'use_kthread' undeclared (first use in this function)
     273 |         if (use_kthread) {
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c:273:13: note: each undeclared identifier is reported only once for each function it appears in
   drivers/vhost/vhost.c: In function 'vhost_workers_free':
   drivers/vhost/vhost.c:805:13: error: 'use_kthread' undeclared (first use in this function)
     805 |         if (use_kthread)
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c: In function 'vhost_worker_create':
   drivers/vhost/vhost.c:986:13: error: 'use_kthread' undeclared (first use in this function)
     986 |         if (use_kthread)
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c: In function 'vhost_free_worker':
   drivers/vhost/vhost.c:1030:13: error: 'use_kthread' undeclared (first use in this function)
    1030 |         if (use_kthread)
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c: In function 'vhost_worker_create':
>> drivers/vhost/vhost.c:990:1: warning: control reaches end of non-void function [-Wreturn-type]
     990 | }
         | ^


vim +990 drivers/vhost/vhost.c

   983	
   984	static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
   985	{
   986		if (use_kthread)
   987			return vhost_worker_create_kthread(dev);
   988		else
   989			return vhost_worker_create_task(dev);
 > 990	}
   991	

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