Re: [Xen-devel] [PATCH] xen/gntdev: fix up blockable calls to mn_invl_range_start

[Michal Hocko <mhocko@xxxxxxxxxx>]

On Thu 23-08-18 22:44:07, Tetsuo Handa wrote:
> On 2018/08/23 21:07, Michal Hocko wrote:
> > diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> > index 57390c7666e5..e7d8bb1bee2a 100644
> > --- a/drivers/xen/gntdev.c
> > +++ b/drivers/xen/gntdev.c
> > @@ -519,21 +519,20 @@ static int mn_invl_range_start(struct mmu_notifier 
> > *mn,
> >     struct gntdev_grant_map *map;
> >     int ret = 0;
> >  
> > -   /* TODO do we really need a mutex here? */
> >     if (blockable)
> >             mutex_lock(&priv->lock);
> >     else if (!mutex_trylock(&priv->lock))
> >             return -EAGAIN;
> >  
> >     list_for_each_entry(map, &priv->maps, next) {
> > -           if (in_range(map, start, end)) {
> > +           if (!blockable && in_range(map, start, end)) {
> 
> This still looks strange. Prior to 93065ac753e4, in_range() test was
> inside unmap_if_in_range(). But this patch removes in_range() test
> if blockable == true. That is, unmap_if_in_range() will unconditionally
> unmap if blockable == true, which seems to be an unexpected change.

You are right. I completely forgot I've removed in_range there. Does
this look any better?

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index e7d8bb1bee2a..30f81004ea63 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -525,14 +525,20 @@ static int mn_invl_range_start(struct mmu_notifier *mn,
                return -EAGAIN;
 
        list_for_each_entry(map, &priv->maps, next) {
-               if (!blockable && in_range(map, start, end)) {
+               if (in_range(map, start, end)) {
+                       if (blockable)
+                               continue;
+
                        ret = -EAGAIN;
                        goto out_unlock;
                }
                unmap_if_in_range(map, start, end);
        }
        list_for_each_entry(map, &priv->freeable_maps, next) {
-               if (!blockable && in_range(map, start, end)) {
+               if (in_range(map, start, end)) {
+                       if (blockable)
+                               continue;
+                       
                        ret = -EAGAIN;
                        goto out_unlock;
                }
-- 
Michal Hocko
SUSE Labs

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