Add back the previously removed cgroup function to support the kthread
The biggest change for this part is in vhost_attach_cgroups() and
vhost_attach_task_to_cgroups().

Reuse the function __vhost_worker_flush, but in this situation, the
attachment_cnt is 0. Therefore, add a boolean to disable this check.

The old function was remove in
commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c | 42 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 37 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 1feba29abf95..adbb957c8b5f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -22,6 +22,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/kthread.h>
+#include <linux/cgroup.h>
 #include <linux/module.h>
 #include <linux/sort.h>
 #include <linux/sched/mm.h>
@@ -269,11 +270,12 @@ EXPORT_SYMBOL_GPL(vhost_vq_work_queue);
  *
  * The worker's flush_mutex must be held.
  */
-static void __vhost_worker_flush(struct vhost_worker *worker)
+static void __vhost_worker_flush(struct vhost_worker *worker,
+				 bool ignore_attachment)
 {
 	struct vhost_flush_struct flush;
 
-	if (!worker->attachment_cnt || worker->killed)
+	if ((!ignore_attachment && !worker->attachment_cnt) || worker->killed)
 		return;
 
 	init_completion(&flush.wait_event);
@@ -292,7 +294,7 @@ static void __vhost_worker_flush(struct vhost_worker *worker)
 static void vhost_worker_flush(struct vhost_worker *worker)
 {
 	mutex_lock(&worker->mutex);
-	__vhost_worker_flush(worker);
+	__vhost_worker_flush(worker, false);
 	mutex_unlock(&worker->mutex);
 }
 
@@ -620,6 +622,36 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
 }
 EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
 
+struct vhost_attach_cgroups_struct {
+	struct vhost_work work;
+	struct task_struct *owner;
+	int ret;
+};
+
+static void vhost_attach_cgroups_work(struct vhost_work *work)
+{
+	struct vhost_attach_cgroups_struct *s;
+
+	s = container_of(work, struct vhost_attach_cgroups_struct, work);
+	s->ret = cgroup_attach_task_all(s->owner, current);
+}
+
+static int vhost_attach_task_to_cgroups(struct vhost_worker *worker)
+{
+	struct vhost_attach_cgroups_struct attach;
+
+	attach.owner = current;
+
+	vhost_work_init(&attach.work, vhost_attach_cgroups_work);
+	vhost_worker_queue(worker, &attach.work);
+
+	mutex_lock(&worker->mutex);
+	__vhost_worker_flush(worker, true);
+	mutex_unlock(&worker->mutex);
+
+	return attach.ret;
+}
+
 /* Caller should have device mutex */
 bool vhost_dev_has_owner(struct vhost_dev *dev)
 {
@@ -793,7 +825,7 @@ static void __vhost_vq_attach_worker(struct vhost_virtqueue *vq,
 	/* Make sure new vq queue/flush/poll calls see the new worker */
 	synchronize_rcu();
 	/* Make sure whatever was queued gets run */
-	__vhost_worker_flush(old_worker);
+	__vhost_worker_flush(old_worker, false);
 	old_worker->attachment_cnt--;
 	mutex_unlock(&old_worker->mutex);
 }
@@ -852,7 +884,7 @@ static int vhost_free_worker(struct vhost_dev *dev,
 	 * to zero. Make sure flushes are flushed from the queue before
 	 * freeing.
 	 */
-	__vhost_worker_flush(worker);
+	__vhost_worker_flush(worker, false);
 	mutex_unlock(&worker->mutex);
 
 	vhost_worker_destroy(dev, worker);
-- 
2.45.0

Hi Cindy,

kernel test robot noticed the following build warnings:

[auto build test WARNING on v6.14-rc3]
[also build test WARNING on linus/master next-20250224]
[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-parameter-in-vhost_dev-to-allow-user-select-kthread/20250223-234405
base:   v6.14-rc3
patch link:    https://lore.kernel.org/r/20250223154042.556001-4-lulu%40redhat.com
patch subject: [PATCH v6 3/6] vhost: Add the cgroup related function
config: x86_64-buildonly-randconfig-002-20250224 (https://download.01.org/0day-ci/archive/20250225/202502251038.6UlCIMJy-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250225/202502251038.6UlCIMJy-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/202502251038.6UlCIMJy-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/vhost/vhost.c:275: warning: Function parameter or struct member 'ignore_attachment' not described in '__vhost_worker_flush'


vim +275 drivers/vhost/vhost.c

0921dddcb589803 Mike Christie 2023-06-26  266  
228a27cf78afc63 Mike Christie 2023-06-26  267  /**
ba704ff4e142fd3 Mike Christie 2024-03-15  268   * __vhost_worker_flush - flush a worker
228a27cf78afc63 Mike Christie 2023-06-26  269   * @worker: worker to flush
228a27cf78afc63 Mike Christie 2023-06-26  270   *
ba704ff4e142fd3 Mike Christie 2024-03-15  271   * The worker's flush_mutex must be held.
228a27cf78afc63 Mike Christie 2023-06-26  272   */
84e88426e3bc18f Cindy Lu      2025-02-23  273  static void __vhost_worker_flush(struct vhost_worker *worker,
84e88426e3bc18f Cindy Lu      2025-02-23  274  				 bool ignore_attachment)
a6fc04739be7cd8 Mike Christie 2023-06-26 @275  {
228a27cf78afc63 Mike Christie 2023-06-26  276  	struct vhost_flush_struct flush;
228a27cf78afc63 Mike Christie 2023-06-26  277  
84e88426e3bc18f Cindy Lu      2025-02-23  278  	if ((!ignore_attachment && !worker->attachment_cnt) || worker->killed)
ba704ff4e142fd3 Mike Christie 2024-03-15  279  		return;
ba704ff4e142fd3 Mike Christie 2024-03-15  280  
228a27cf78afc63 Mike Christie 2023-06-26  281  	init_completion(&flush.wait_event);
228a27cf78afc63 Mike Christie 2023-06-26  282  	vhost_work_init(&flush.work, vhost_flush_work);
228a27cf78afc63 Mike Christie 2023-06-26  283  
228a27cf78afc63 Mike Christie 2023-06-26  284  	vhost_worker_queue(worker, &flush.work);
ba704ff4e142fd3 Mike Christie 2024-03-15  285  	/*
ba704ff4e142fd3 Mike Christie 2024-03-15  286  	 * Drop mutex in case our worker is killed and it needs to take the
ba704ff4e142fd3 Mike Christie 2024-03-15  287  	 * mutex to force cleanup.
ba704ff4e142fd3 Mike Christie 2024-03-15  288  	 */
ba704ff4e142fd3 Mike Christie 2024-03-15  289  	mutex_unlock(&worker->mutex);
228a27cf78afc63 Mike Christie 2023-06-26  290  	wait_for_completion(&flush.wait_event);
ba704ff4e142fd3 Mike Christie 2024-03-15  291  	mutex_lock(&worker->mutex);
ba704ff4e142fd3 Mike Christie 2024-03-15  292  }
ba704ff4e142fd3 Mike Christie 2024-03-15  293  

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

On Sun, Feb 23, 2025 at 11:41 PM Cindy Lu <lulu@redhat.com> wrote:
>
> Add back the previously removed cgroup function to support the kthread
> The biggest change for this part is in vhost_attach_cgroups() and
> vhost_attach_task_to_cgroups().
>
> Reuse the function __vhost_worker_flush, but in this situation, the
> attachment_cnt is 0. Therefore, add a boolean to disable this check.
>

How about just tweaking its value to INT_MAX so we can avoid this new parameter?

Thanks

On Mon, Feb 24, 2025 at 9:40 AM Jason Wang <jasowang@redhat.com> wrote:
>
> On Sun, Feb 23, 2025 at 11:41 PM Cindy Lu <lulu@redhat.com> wrote:
> >
> > Add back the previously removed cgroup function to support the kthread
> > The biggest change for this part is in vhost_attach_cgroups() and
> > vhost_attach_task_to_cgroups().
> >
> > Reuse the function __vhost_worker_flush, but in this situation, the
> > attachment_cnt is 0. Therefore, add a boolean to disable this check.
> >
>
> How about just tweaking its value to INT_MAX so we can avoid this new parameter?
>
> Thanks
>
sure, will change this
thanks
cindy