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

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

[Gautam Dawar]

From: Gautam Dawar <gdawar@xilinx.com>

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@xilinx.com>
---
 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);
-- 
2.30.1

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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@xilinx.com>
>
> 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@xilinx.com>
> ---
>   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@redhat.com>


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

[Michael S. Tsirkin]

On Tue, Jun 15, 2021 at 10:33:22PM +0800, Jason Wang wrote:
> 
> 在 2021/6/6 下午9:29, Gautam Dawar 写道:
> > From: Gautam Dawar <gdawar@xilinx.com>
> > 
> > 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@xilinx.com>
> > ---
> >   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));

Can fill up the kernel log in this case ... dev_warn_once seems more
appropriate.

> >   	} while (1);
> >   	put_device(&v->dev);
> 
> 
> Acked-by: Jason Wang <jasowang@redhat.com>
> 

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