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* [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked
@ 2021-06-06 13:29 Gautam Dawar
  2021-06-15 14:33 ` Jason Wang
  2021-07-03 19:01 ` gautam.dawar
  0 siblings, 2 replies; 5+ messages in thread
From: Gautam Dawar @ 2021-06-06 13:29 UTC (permalink / raw)
  Cc: martinh, hanand, gdawar, Michael S. Tsirkin, Jason Wang, kvm,
	virtualization, netdev, linux-kernel

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


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked
  2021-06-06 13:29 [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked Gautam Dawar
@ 2021-06-15 14:33 ` Jason Wang
  2021-07-03  8:11   ` Michael S. Tsirkin
  2021-07-03 19:01 ` gautam.dawar
  1 sibling, 1 reply; 5+ messages in thread
From: Jason Wang @ 2021-06-15 14:33 UTC (permalink / raw)
  To: Gautam Dawar
  Cc: martinh, hanand, gdawar, Michael S. Tsirkin, kvm, virtualization,
	netdev, linux-kernel


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>



^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked
  2021-06-15 14:33 ` Jason Wang
@ 2021-07-03  8:11   ` Michael S. Tsirkin
  2021-07-03 19:08     ` Gautam Dawar
  0 siblings, 1 reply; 5+ messages in thread
From: Michael S. Tsirkin @ 2021-07-03  8:11 UTC (permalink / raw)
  To: Jason Wang
  Cc: Gautam Dawar, martinh, hanand, gdawar, kvm, virtualization,
	netdev, linux-kernel

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>
> 


^ permalink raw reply	[flat|nested] 5+ messages in thread

* [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked
  2021-06-06 13:29 [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked Gautam Dawar
  2021-06-15 14:33 ` Jason Wang
@ 2021-07-03 19:01 ` gautam.dawar
  1 sibling, 0 replies; 5+ messages in thread
From: gautam.dawar @ 2021-07-03 19:01 UTC (permalink / raw)
  Cc: martinh, hanand, gdawar, Jason Wang, Michael S. Tsirkin, kvm,
	virtualization, netdev, linux-kernel

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>
Acked-by: Jason Wang <jasowang@redhat.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..e4b7d26649d8 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_once(&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


^ permalink raw reply	[flat|nested] 5+ messages in thread

* RE: [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked
  2021-07-03  8:11   ` Michael S. Tsirkin
@ 2021-07-03 19:08     ` Gautam Dawar
  0 siblings, 0 replies; 5+ messages in thread
From: Gautam Dawar @ 2021-07-03 19:08 UTC (permalink / raw)
  To: Michael S. Tsirkin, Jason Wang
  Cc: Gautam Dawar, Martin Petrus Hubertus Habets,
	Harpreet Singh Anand, kvm, virtualization, netdev, linux-kernel

Pls see inline [GD>>]

-----Original Message-----
From: Michael S. Tsirkin <mst@redhat.com> 
Sent: Saturday, July 3, 2021 1:42 PM
To: Jason Wang <jasowang@redhat.com>
Cc: Gautam Dawar <gdawar.xilinx@gmail.com>; Martin Petrus Hubertus Habets <martinh@xilinx.com>; Harpreet Singh Anand <hanand@xilinx.com>; Gautam Dawar <gdawar@xilinx.com>; kvm@vger.kernel.org; virtualization@lists.linux-foundation.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked

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.
[GD>>] Submitted the patch with suggested modification.

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


^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2021-07-03 19:21 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2021-06-06 13:29 [PATCH] vhost-vdpa: log warning message if vhost_vdpa_remove gets blocked Gautam Dawar
2021-06-15 14:33 ` Jason Wang
2021-07-03  8:11   ` Michael S. Tsirkin
2021-07-03 19:08     ` Gautam Dawar
2021-07-03 19:01 ` gautam.dawar

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