Pls see inline [GD>>] -----Original Message----- From: Michael S. Tsirkin <mst@xxxxxxxxxx> Sent: Saturday, July 3, 2021 1:42 PM To: Jason Wang <jasowang@xxxxxxxxxx> Cc: Gautam Dawar <gdawar.xilinx@xxxxxxxxx>; Martin Petrus Hubertus Habets <martinh@xxxxxxxxxx>; Harpreet Singh Anand <hanand@xxxxxxxxxx>; Gautam Dawar <gdawar@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx 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@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)); 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@xxxxxxxxxx> >
