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

From: Veaceslav Falico
Date: Tue Oct 29 2013 - 12:50:07 EST

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) {
+ } 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


work for the "not registered with sysfs" case? And if the sysfs code
really gets confused, why not

if (entry->kobj.parent)

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

struct sysfs_dirent *sd = kobj->sd;

kobj->sd = NULL;

and I would suggest that "sd = kobj->sd" should be done under the
lock, because otherwise the lock is kind of pointless..)


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