Re: [PATCH v3 1/3] msi: free msi_desc entry only after we'vereleased the kobject

[Veaceslav Falico]

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@xxxxxxxxxx> 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);

It was fixed this way in 424eb39 ("PCI: msi: fix imbalanced refcount of msi
irq sysfs objects"). kobject_put() still failed in case it wasn't
registered with sysfs earlier. populate_msi_sysfs() creates an kobject for
each entry in msi_list, and we have no idea (on fallback) up to which entry
was it already registered, on which it failed and which entries are still
not kobject_init_and_add()ed.

> (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?
>
>                Linus
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