Linux Virtualization - Sep 2019 - [PATCH 08/18] virtiofs: Drain all pending requests during ->remove time

On Thu, Sep 05, 2019 at 03:48:49PM -0400, Vivek Goyal
wrote:
> +static void virtio_fs_drain_queue(struct virtio_fs_vq *fsvq)
> +{
> +	WARN_ON(fsvq->in_flight < 0);
> +
> +	/* Wait for in flight requests to finish.*/
> +	while (1) {
> +		spin_lock(&fsvq->lock);
> +		if (!fsvq->in_flight) {
> +			spin_unlock(&fsvq->lock);
> +			break;
> +		}
> +		spin_unlock(&fsvq->lock);
> +		usleep_range(1000, 2000);
> +	}
I think all contexts that call this allow sleeping so we could avoid
usleep here.
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On Fri, Sep 06, 2019 at 11:52:10AM +0100, Stefan Hajnoczi
wrote:
> On Thu, Sep 05, 2019 at 03:48:49PM -0400, Vivek Goyal wrote:
> > +static void virtio_fs_drain_queue(struct virtio_fs_vq *fsvq)
> > +{
> > +	WARN_ON(fsvq->in_flight < 0);
> > +
> > +	/* Wait for in flight requests to finish.*/
> > +	while (1) {
> > +		spin_lock(&fsvq->lock);
> > +		if (!fsvq->in_flight) {
> > +			spin_unlock(&fsvq->lock);
> > +			break;
> > +		}
> > +		spin_unlock(&fsvq->lock);
> > +		usleep_range(1000, 2000);
> > +	}
> 
> I think all contexts that call this allow sleeping so we could avoid
> usleep here.
usleep_range() is supposed to be used from non-atomic context.

https://github.com/torvalds/linux/blob/master/Documentation/timers/timers-howto.rst

What construct you are thinking of?

Vivek

On Fri, Sep 06, 2019 at 10:17:05AM -0400, Vivek Goyal
wrote:
> On Fri, Sep 06, 2019 at 11:52:10AM +0100, Stefan Hajnoczi wrote:
> > On Thu, Sep 05, 2019 at 03:48:49PM -0400, Vivek Goyal wrote:
> > > +static void virtio_fs_drain_queue(struct virtio_fs_vq *fsvq)
> > > +{
> > > +	WARN_ON(fsvq->in_flight < 0);
> > > +
> > > +	/* Wait for in flight requests to finish.*/
> > > +	while (1) {
> > > +		spin_lock(&fsvq->lock);
> > > +		if (!fsvq->in_flight) {
> > > +			spin_unlock(&fsvq->lock);
> > > +			break;
> > > +		}
> > > +		spin_unlock(&fsvq->lock);
> > > +		usleep_range(1000, 2000);
> > > +	}
> > 
> > I think all contexts that call this allow sleeping so we could avoid
> > usleep here.
> 
> usleep_range() is supposed to be used from non-atomic context.
> 
>
https://github.com/torvalds/linux/blob/master/Documentation/timers/timers-howto.rst
> 
> What construct you are thinking of?
> 
> Vivek
completion + signal on vq callback?

-- 
MST