Virtualization - May 2023 - [RFC PATCH 2/8] vhost/vhost_task: Hook vhost layer into signal handler

This patch has vhost use get_signal to handle freezing and sort of
handle signals. By the latter I mean that when we get SIGKILL, our
parent will exit and call our file_operatons release function. That will
then stop new work from breing queued and wait for the vhost_task to
handle completions for running IO. We then exit when those are done.

The next patches will then have us work more like io_uring where
we handle the get_signal return value and key off that to cleanup.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
---
 drivers/vhost/vhost.c            | 10 +++++++++-
 include/linux/sched/vhost_task.h |  1 +
 kernel/vhost_task.c              | 20 ++++++++++++++++++++
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index a92af08e7864..1ba9e068b2ab 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -349,8 +349,16 @@ static int vhost_worker(void *data)
 		}
 
 		node = llist_del_all(&worker->work_list);
-		if (!node)
+		if (!node) {
 			schedule();
+			/*
+			 * When we get a SIGKILL our release function will
+			 * be called. That will stop new IOs from being queued
+			 * and check for outstanding cmd responses. It will then
+			 * call vhost_task_stop to exit us.
+			 */
+			vhost_task_get_signal();
+		}
 
 		node = llist_reverse_order(node);
 		/* make sure flag is seen after deletion */
diff --git a/include/linux/sched/vhost_task.h b/include/linux/sched/vhost_task.h
index 6123c10b99cf..54b68115eb3b 100644
--- a/include/linux/sched/vhost_task.h
+++ b/include/linux/sched/vhost_task.h
@@ -19,5 +19,6 @@ struct vhost_task *vhost_task_create(int (*fn)(void *), void
*arg,
 void vhost_task_start(struct vhost_task *vtsk);
 void vhost_task_stop(struct vhost_task *vtsk);
 bool vhost_task_should_stop(struct vhost_task *vtsk);
+bool vhost_task_get_signal(void);
 
 #endif
diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c
index b7cbd66f889e..a661cfa32ba3 100644
--- a/kernel/vhost_task.c
+++ b/kernel/vhost_task.c
@@ -61,6 +61,26 @@ bool vhost_task_should_stop(struct vhost_task *vtsk)
 }
 EXPORT_SYMBOL_GPL(vhost_task_should_stop);
 
+/**
+ * vhost_task_get_signal - Check if there are pending signals
+ *
+ * Return true if we got SIGKILL.
+ */
+bool vhost_task_get_signal(void)
+{
+	struct ksignal ksig;
+	bool rc;
+
+	if (!signal_pending(current))
+		return false;
+
+	__set_current_state(TASK_RUNNING);
+	rc = get_signal(&ksig);
+	set_current_state(TASK_INTERRUPTIBLE);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(vhost_task_get_signal);
+
 /**
  * vhost_task_create - create a copy of a process to be used by the kernel
  * @fn: thread stack
-- 
2.25.1

On Wed, May 17, 2023 at 5:09?PM Mike Christie
<michael.christie at oracle.com> wrote:
>
> +       __set_current_state(TASK_RUNNING);
> +       rc = get_signal(&ksig);
> +       set_current_state(TASK_INTERRUPTIBLE);
> +       return rc;
The games with current_state seem nonsensical.

What are they all about? get_signal() shouldn't care, and no other
caller does this thing. This just seems completely random.

      Linus