Re: [Xen-devel] [PATCHv4 10/14] xen/gntdev: convert priv->lock to a mutex

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 26 Jan 2015, David Vrabel wrote:
> On 26/01/15 18:57, Stefano Stabellini wrote:
> > 
> >> @@ -443,14 +443,14 @@ static void mn_invl_range_start(struct mmu_notifier 
> >> *mn,
> >>    struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
> >>    struct grant_map *map;
> >>  
> >> -  spin_lock(&priv->lock);
> >> +  mutex_lock(&priv->lock);
> >>    list_for_each_entry(map, &priv->maps, next) {
> >>            unmap_if_in_range(map, start, end);
> >>    }
> >>    list_for_each_entry(map, &priv->freeable_maps, next) {
> >>            unmap_if_in_range(map, start, end);
> >>    }
> >> -  spin_unlock(&priv->lock);
> >> +  mutex_unlock(&priv->lock);
> >>  }
> > 
> > I don't think that mmu_notifier callbacks are allowed to sleep:
> > 
> > https://lkml.org/lkml/2010/1/25/187
> 
> I don't think that limitation exists any more.  SRCU is used and you can
> sleep between tlb_gather_mmu()/tlb_finish_mmu().
> 
> Perhaps you could point to something that isn't 5 years old?

Point taken.

However the problem is that I couldn't find anything that points in the
other direction either. If you look at include/linux/mmu_notifier.h, it
doesn't state that the callbacks can sleep, except for:

 * The invalidate_range() function is called under the ptl
 * spin-lock and not allowed to sleep.

Therefore maybe we can assume that the others are allowed to sleep,
because there are no comments about it?

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