On Fri, 04 Mar 2022, Leon Romanovsky wrote:
> On Thu, Mar 03, 2022 at 04:01:06PM -0500, Michael S. Tsirkin wrote:
> > On Thu, Mar 03, 2022 at 09:14:36PM +0200, Leon Romanovsky wrote:
> > > On Thu, Mar 03, 2022 at 03:19:29PM +0000, Lee Jones wrote:
> > > > All workers/users should be halted before any clean-up should take place.
> > > >
> > > > Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > > > ---
> > > > drivers/vhost/vhost.c | 3 +++
> > > > 1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > > index bbaff6a5e21b8..d935d2506963f 100644
> > > > --- a/drivers/vhost/vhost.c
> > > > +++ b/drivers/vhost/vhost.c
> > > > @@ -693,6 +693,9 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > > > int i;
> > > >
> > > > for (i = 0; i < dev->nvqs; ++i) {
> > > > + /* Ideally all workers should be stopped prior to clean-up */
> > > > + WARN_ON(mutex_is_locked(&dev->vqs[i]->mutex));
> > > > +
> > > > mutex_lock(&dev->vqs[i]->mutex);
HERE ---^
> > > I know nothing about vhost, but this construction and patch looks
> > > strange to me.
> > >
> > > If all workers were stopped, you won't need mutex_lock(). The mutex_lock
> > > here suggests to me that workers can still run here.
> > >
> > > Thanks
> >
> >
> > "Ideally" here is misleading, we need a bigger detailed comment
> > along the lines of:
> >
> > /*
> > * By design, no workers can run here. But if there's a bug and the
> > * driver did not flush all work properly then they might, and we
> > * encountered such bugs in the past. With no proper flush guest won't
> > * work correctly but avoiding host memory corruption in this case
> > * sounds like a good idea.
> > */
>
> This description looks better, but the check is inherently racy.
> Why don't you add a comment and mutex_lock()?
We do, look up. ^
> The WARN_ON here is more distraction than actual help.
The WARN() is just an indication that something else has gone wrong.
Stefano patched one problem in:
vhost: Protect the virtqueue from being cleared whilst still in use
... but others may crop up and the WARN() is how we'll be informed.
--
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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