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

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