From d2be773a92874a070215b51b730cb2b1eaa8fae2 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Thu, 18 Sep 2025 20:11:44 +0200 Subject: [PATCH] vhost: Take a reference on the task in struct vhost_task. [ Upstream commit afe16653e05db07d658b55245c7a2e0603f136c0 ] vhost_task_create() creates a task and keeps a reference to its task_struct. That task may exit early via a signal and its task_struct will be released. A pending vhost_task_wake() will then attempt to wake the task and access a task_struct which is no longer there. Acquire a reference on the task_struct while creating the thread and release the reference while the struct vhost_task itself is removed. If the task exits early due to a signal, then the vhost_task_wake() will still access a valid task_struct. The wake is safe and will be skipped in this case. Fixes: f9010dbdce911 ("fork, vhost: Use CLONE_THREAD to fix freezer/ps regression") Reported-by: Sean Christopherson Closes: https://lore.kernel.org/all/aKkLEtoDXKxAAWju@google.com/ Signed-off-by: Sebastian Andrzej Siewior Message-Id: <20250918181144.Ygo8BZ-R@linutronix.de> Signed-off-by: Michael S. Tsirkin Tested-by: Sean Christopherson Signed-off-by: Sasha Levin --- kernel/vhost_task.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c index 2f844c279a3e..7f24ccc896c6 100644 --- a/kernel/vhost_task.c +++ b/kernel/vhost_task.c @@ -100,6 +100,7 @@ void vhost_task_stop(struct vhost_task *vtsk) * freeing it below. */ wait_for_completion(&vtsk->exited); + put_task_struct(vtsk->task); kfree(vtsk); } EXPORT_SYMBOL_GPL(vhost_task_stop); @@ -148,7 +149,7 @@ struct vhost_task *vhost_task_create(bool (*fn)(void *), return ERR_PTR(PTR_ERR(tsk)); } - vtsk->task = tsk; + vtsk->task = get_task_struct(tsk); return vtsk; } EXPORT_SYMBOL_GPL(vhost_task_create);