Re: [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked

[Jason Wang]

在 2021/6/6 下午9:29, Gautam Dawar 写道:
> From: Gautam Dawar <gdawar@xxxxxxxxxx>
>
> If some module invokes vdpa_device_unregister (usually in the module
> unload function) when the userspace app (eg. QEMU) which had opened
> the vhost-vdpa character device is still running, vhost_vdpa_remove()
> function will block indefinitely in call to wait_for_completion().
>
> This causes the vdpa_device_unregister caller to hang and with a
> usual side-effect of rmmod command not returning when this call
> is in the module_exit function.
>
> This patch converts the wait_for_completion call to its timeout based
> counterpart (wait_for_completion_timeout) and also adds a warning
> message to alert the user/administrator about this hang situation.
>
> To eventually fix this problem, a mechanism will be required to let
> vhost-vdpa module inform the userspace of this situation and
> userspace will close the descriptor of vhost-vdpa char device.
> This will enable vhost-vdpa to continue with graceful clean-up.
>
> Signed-off-by: Gautam Dawar <gdawar@xxxxxxxxxx>
> ---
>   drivers/vhost/vdpa.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index bfa4c6ef554e..572b64d09b06 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -1091,7 +1091,11 @@ static void vhost_vdpa_remove(struct vdpa_device *vdpa)
>   		opened = atomic_cmpxchg(&v->opened, 0, 1);
>   		if (!opened)
>   			break;
> -		wait_for_completion(&v->completion);
> +		wait_for_completion_timeout(&v->completion,
> +					    msecs_to_jiffies(1000));
> +		dev_warn_ratelimited(&v->dev,
> +				     "%s waiting for /dev/%s to be closed\n",
> +				     __func__, dev_name(&v->dev));
>   	} while (1);
>   
>   	put_device(&v->dev);


Acked-by: Jason Wang <jasowang@xxxxxxxxxx>