On Wed, 16 May 2018 11:05:06 +0200 Cornelia Huck <[email protected]> wrote:
> On Tue, 15 May 2018 14:17:04 -0600 > Alex Williamson <[email protected]> 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 <[email protected]> > > --- > > 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
