On Wed, 16 May 2018 11:05:06 +0200
Cornelia Huck <cohuck@xxxxxxxxxx> wrote:
> On Tue, 15 May 2018 14:17:04 -0600
> Alex Williamson <alex.williamson@xxxxxxxxxx> wrote:
>
> > When we create an mdev device, we check for duplicates against the
> > parent device and return -EEXIST if found, but the mdev device
> > namespace is global since we'll link all devices from the bus. We do
> > catch this later in sysfs_do_create_link_sd() to return -EEXIST, but
> > with it comes a kernel warning and stack trace for trying to create
> > duplicate sysfs links, which makes it an undesirable response.
> >
> > Therefore we should really be looking for duplicates across all mdev
> > parent devices, or as implemented here, against our mdev device list.
> >
> > Notably, mdev_parent.lock really only seems to be serializing device
> > creation and removal per parent. I'm not sure if this is necessary,
> > mdev vendor drivers could easily provide this serialization if it
> > is required, but a side-effect of holding the mdev_list_lock to
> > protect the namespace is actually greater serialization across the
> > create and remove paths, so mdev_parent.lock is removed. If we can
> > show that vendor drivers handle the create/remove paths themselves,
> > perhaps we can refine the locking granularity.
>
> I'm not sure whether more locking granularity on the create/remove
> paths is really worth the effort.
Perhaps not, but I thought I should at least mention it as a
consideration.
> > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > ---
> > drivers/vfio/mdev/mdev_core.c | 79 ++++++++++----------------------------
> > drivers/vfio/mdev/mdev_private.h | 1
> > 2 files changed, 20 insertions(+), 60 deletions(-)
>
> In general, I think this patch makes sense; some nits below.
>
> >
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index 126991046eb7..3d8898a2baaf 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
>
> > @@ -376,12 +346,13 @@ int mdev_device_remove(struct device *dev, bool force_remove)
> > struct mdev_device *mdev, *tmp;
> > struct mdev_parent *parent;
> > struct mdev_type *type;
> > - int ret;
> > + int ret = 0;
>
> I don't think you need to init this, as ret should either be set to
> -ENODEV or the return code of mdev_device_remove_ops(), shouldn't it?
Yep, I think this is a leftover from before I decided I should goto a
common out, it's unnecessary now. Removed.
> > bool found = false;
> >
> > mdev = to_mdev_device(dev);
> >
> > mutex_lock(&mdev_list_lock);
> > +
>
> unrelated whitespace change
Intentional, previously mdev_list_lock was only protecting this
sub-section of the code, so the lock was tucked up to it. Now we're
holding the lock across the whole function so I wanted to make it
separate.
> > list_for_each_entry(tmp, &mdev_list, next) {
> > if (tmp == mdev) {
> > found = true;
> > @@ -389,35 +360,25 @@ int mdev_device_remove(struct device *dev, bool force_remove)
> > }
> > }
> >
> > - if (found)
> > - list_del(&mdev->next);
> > -
> > - mutex_unlock(&mdev_list_lock);
> > -
> > - if (!found)
> > - return -ENODEV;
> > + if (!found) {
> > + ret = -ENODEV;
> > + goto out;
> > + }
> >
> > type = to_mdev_type(mdev->type_kobj);
> > parent = mdev->parent;
> > - mutex_lock(&parent->lock);
> >
> > ret = mdev_device_remove_ops(mdev, force_remove);
> > - if (ret) {
> > - mutex_unlock(&parent->lock);
> > -
> > - mutex_lock(&mdev_list_lock);
> > - list_add(&mdev->next, &mdev_list);
> > - mutex_unlock(&mdev_list_lock);
> > -
> > - return ret;
> > - }
> > + if (ret)
> > + goto out;
>
> This change really simplyfies the code, nice.
Agreed, thanks for the review!
Alex
