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SubjectRe: [RFC][PATCH 4/4] configfs: Make multiple default_group destructions lockdep friendly
On Mon, Jun 02, 2008 at 04:07:21PM -0700, Joel Becker wrote:
> A couple comments.
> First, put a BUG_ON() where you have BAD BAD BAD - we shouldn't
> be creating a depth we can't delete.

I think that the best way to avoid this is to use the same numbering scheme
while attaching default groups.

This would change the body of populate_groups() like this:

- if (group->default_groups) {
+ /* lock_level starts at zero for the non default group.
+ * Set it even if we do not take the lock, so that we can use the same
+ * numbering scheme as for destruction time, and can prevent overload at
+ * destruction time. */
+ lock_level = set_dirent_lock_level(parent_sd, sd);
+ if (lock_level < 0) {
+ /* Too many default groups */
+ ret = lock_level;
+ } else if (group->default_groups) {
/*
* FYI, we're faking mkdir here
* I'm not sure we need this semaphore, as we're called
* from our parent's mkdir. That holds our parent's
* i_mutex, so afaik lookup cannot continue through our
* parent to find us, let alone mess with our tree.
* That said, taking our i_mutex is closer to mkdir
* emulation, and shouldn't hurt.
*/
- /* lock_level starts at zero for the non default group */
- lock_level = set_dirent_lock_level(parent_sd, sd);
- if (lock_level < 0) {
- /* Too deeply nested default groups */
- ret = lock_level;
- } else {
mutex_lock_nested(&dentry->d_inode->i_mutex,
I_MUTEX_CHILD + lock_level);
for (i = 0; group->default_groups[i]; i++) {
new_group = group->default_groups[i];
ret = create_default_group(group, new_group);
if (ret)
break;
}
mutex_unlock(&dentry->d_inode->i_mutex);
- /* Reset for future sub-group creations */
- reset_dirent_lock_level(sd);
- }
}
+ if (lock_level > 0)
+ /* Update parent lock_level to keep it increasing, but not
+ * if group is the one actually created/registered by the
+ * user/subsystem */
+ copy_dirent_lock_level(sd, parent_sd);
+ /* Reset for future sub-group creations */
+ reset_dirent_lock_level(sd);
>
> > @@ -392,6 +437,10 @@ static int configfs_detach_prep(struct d
> > * deep nesting of default_groups
> > */
> > ret = configfs_detach_prep(sd->s_dentry);
> > + /* Update parent's lock_level so that remaining
> > + * sibling children keep on globally increasing
> > + * lock_level */
> > + copy_dirent_lock_level(sd, parent_sd);
> > if (!ret)
> > continue;
> > } else
>
> I'm not sure I get this hunk. If our parent was 1 and we are 2,
> we are copying 2 to our parent so the parent can only have other
> children at 3?

Exactly.

Louis

--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes

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