[PATCH] vhost: clear vq->worker under vq->mutex when freeing workers

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

Every other update of vq->worker is done under vq->mutex - the worker
attach/swap ioctls and vhost_worker_killed().  vhost_workers_free() is
the sole exception: it clears vq->worker without holding the lock.

The effect is harmless in practice, as this only happens while the
owning process (and thus the whole device) is dying, but the lockless
write is inconsistent with the rest of the code.  Clear vq->worker under
vq->mutex, like everyone else, so that all writers of vq->worker follow
the same locking rule.

This issue was found by Sashiko AI review.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 drivers/vhost/vhost.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 4c525b3e16ea..dbb6cb5eccea 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -722,13 +722,19 @@ static void vhost_worker_destroy(struct vhost_dev *dev,
 static void vhost_workers_free(struct vhost_dev *dev)
 {
 	struct vhost_worker *worker;
+	struct vhost_virtqueue *vq;
 	unsigned long i;
 
 	if (!dev->use_worker)
 		return;
 
-	for (i = 0; i < dev->nvqs; i++)
-		rcu_assign_pointer(dev->vqs[i]->worker, NULL);
+	for (i = 0; i < dev->nvqs; i++) {
+		vq = dev->vqs[i];
+
+		mutex_lock(&vq->mutex);
+		rcu_assign_pointer(vq->worker, NULL);
+		mutex_unlock(&vq->mutex);
+	}
 	/*
 	 * Free the default worker we created and cleanup workers userspace
 	 * created but couldn't clean up (it forgot or crashed).
-- 
2.47.1