vhost_task: Handle SIGKILL by flushing work and exiting

Instead of lingering until the device is closed, this has us handle
SIGKILL by:

1. marking the worker as killed so we no longer try to use it with
   new virtqueues and new flush operations.
2. setting the virtqueue to worker mapping so no new works are queued.
3. running all the exiting works.

Suggested-by: Edward Adam Davis <eadavis@qq.com>
Reported-and-tested-by: syzbot+98edc2df894917b3431f@syzkaller.appspotmail.com
Message-Id: <tencent_546DA49414E876EEBECF2C78D26D242EE50A@qq.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20240316004707.45557-9-michael.christie@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 52 insertions, 4 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c6448ff37768..b60955682474 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -273,7 +273,7 @@ static void __vhost_worker_flush(struct vhost_worker *worker)
 {
 	struct vhost_flush_struct flush;
 
-	if (!worker->attachment_cnt)
+	if (!worker->attachment_cnt || worker->killed)
 		return;
 
 	init_completion(&flush.wait_event);
@@ -388,7 +388,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	__vhost_vq_meta_reset(vq);
 }
 
-static bool vhost_worker(void *data)
+static bool vhost_run_work_list(void *data)
 {
 	struct vhost_worker *worker = data;
 	struct vhost_work *work, *work_next;
@@ -413,6 +413,40 @@ static bool vhost_worker(void *data)
 	return !!node;
 }
 
+static void vhost_worker_killed(void *data)
+{
+	struct vhost_worker *worker = data;
+	struct vhost_dev *dev = worker->dev;
+	struct vhost_virtqueue *vq;
+	int i, attach_cnt = 0;
+
+	mutex_lock(&worker->mutex);
+	worker->killed = true;
+
+	for (i = 0; i < dev->nvqs; i++) {
+		vq = dev->vqs[i];
+
+		mutex_lock(&vq->mutex);
+		if (worker ==
+		    rcu_dereference_check(vq->worker,
+					  lockdep_is_held(&vq->mutex))) {
+			rcu_assign_pointer(vq->worker, NULL);
+			attach_cnt++;
+		}
+		mutex_unlock(&vq->mutex);
+	}
+
+	worker->attachment_cnt -= attach_cnt;
+	if (attach_cnt)
+		synchronize_rcu();
+	/*
+	 * Finish vhost_worker_flush calls and any other works that snuck in
+	 * before the synchronize_rcu.
+	 */
+	vhost_run_work_list(worker);
+	mutex_unlock(&worker->mutex);
+}
+
 static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
 {
 	kfree(vq->indirect);
@@ -627,9 +661,11 @@ static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
 	if (!worker)
 		return NULL;
 
+	worker->dev = dev;
 	snprintf(name, sizeof(name), "vhost-%d", current->pid);
 
-	vtsk = vhost_task_create(vhost_worker, worker, name);
+	vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
+				 worker, name);
 	if (!vtsk)
 		goto free_worker;
 
@@ -661,6 +697,11 @@ static void __vhost_vq_attach_worker(struct vhost_virtqueue *vq,
 	struct vhost_worker *old_worker;
 
 	mutex_lock(&worker->mutex);
+	if (worker->killed) {
+		mutex_unlock(&worker->mutex);
+		return;
+	}
+
 	mutex_lock(&vq->mutex);
 
 	old_worker = rcu_dereference_check(vq->worker,
@@ -681,6 +722,11 @@ static void __vhost_vq_attach_worker(struct vhost_virtqueue *vq,
 	 * device wide flushes which doesn't use RCU for execution.
 	 */
 	mutex_lock(&old_worker->mutex);
+	if (old_worker->killed) {
+		mutex_unlock(&old_worker->mutex);
+		return;
+	}
+
 	/*
 	 * We don't want to call synchronize_rcu for every vq during setup
 	 * because it will slow down VM startup. If we haven't done
@@ -758,7 +804,7 @@ static int vhost_free_worker(struct vhost_dev *dev,
 		return -ENODEV;
 
 	mutex_lock(&worker->mutex);
-	if (worker->attachment_cnt) {
+	if (worker->attachment_cnt || worker->killed) {
 		mutex_unlock(&worker->mutex);
 		return -EBUSY;
 	}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 91ade037f08e..bb75a292d50c 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -28,12 +28,14 @@ struct vhost_work {
 
 struct vhost_worker {
 	struct vhost_task	*vtsk;
+	struct vhost_dev	*dev;
 	/* Used to serialize device wide flushing with worker swapping. */
 	struct mutex		mutex;
 	struct llist_head	work_list;
 	u64			kcov_handle;
 	u32			id;
 	int			attachment_cnt;
+	bool			killed;
 };
 
 /* Poll a file (eventfd or socket) */