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SubjectRe: [PATCH v3 1/3] msi: free msi_desc entry only after we've released the kobject
On Tue, Oct 29, 2013 at 09:34:28AM -0700, Linus Torvalds wrote:
> On Tue, Oct 29, 2013 at 3:30 AM, Veaceslav Falico <vfalico@redhat.com> wrote:
> > /*
> > * Its possible that we get into this path
> > * When populate_msi_sysfs fails, which means the entries
> > * were not registered with sysfs. In that case don't
> > - * unregister them.
> > + * unregister them, and just free. Otherwise the
> > + * kobject->release will take care of freeing the entry via
> > + * msi_kobj_release().
> > */
> > if (entry->kobj.parent) {
> > kobject_del(&entry->kobj);
> > kobject_put(&entry->kobj);
> > + } else {
> > + kfree(entry);
> > }
> > -
> > - list_del(&entry->list);
> > - kfree(entry);
>
> So this code sequence still makes me very unhappy.
>
> Why does not just a simple unconditional
>
> kobject_del(&entry->kobj);
> kobject_put(&entry->kobj);
>
> work for the "not registered with sysfs" case? And if the sysfs code
> really gets confused, why not
>
> if (entry->kobj.parent)
> kobject_del(&entry->kobj);
> kobject_put(&entry->kobj);
>
> (btw, looking at the sysfs code, this looks *very* suspicious in
> sysfs_remove_dir():
>
> struct sysfs_dirent *sd = kobj->sd;
>
> spin_lock(&sysfs_assoc_lock);
> kobj->sd = NULL;
> spin_unlock(&sysfs_assoc_lock);
>
> and I would suggest that "sd = kobj->sd" should be done under the
> lock, because otherwise the lock is kind of pointless..)
>
> Greg?

That is really odd, but I guess it works as-is because no one ever calls
that function on the same kobject at the same time. I don't know what
that is trying to do. There has been some work by Tejun in this area
for linux-next, but that lock and logic is still there, I'll look into
fixing that up...

thanks,

greg k-h


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