On Tue, Oct 23, 2007 at 02:08:19PM -0700, Roland Dreier wrote:
> A few comments:
>
> > + dev_err(port->dev, "PPS support disabled due port \"%s\" is "
> > + "in polling mode\n",
>
> I think "because" instead of "due" is closer to standard English.
Fixed.
> > + printk(KERN_ERR "pps: %s: too much PPS sources in the system\n",
> > + info->name);
>
> Similarly should be "many" instead of "much".
Fixed.
> > + /* Get new ID for the new PPS source */
> > + if (idr_pre_get(&pps_idr, GFP_KERNEL) == 0) {
> > + err = -ENOMEM;
> > + goto kfree_pps;
> > + }
> > +
> > + spin_lock_irq(&idr_lock);
> > + err = idr_get_new(&pps_idr, pps, &id);
> > + spin_unlock_irq(&idr_lock);
> > +
> > + if (err < 0)
> > + goto kfree_pps;
>
> You usually can handle idr_get_new() returning -EAGAIN by jumping back
> to the idr_pre_get(), to handle someone else coming in and stealing
> the memory you just preallocated. In this case it may not matter
> since it's pretty unlikely that a lot of contexts are using the idr at
> the same time. But anyway...
I don't understand what you mean. Can you please submit an example
code?
> > +void pps_unregister_source(int source)
> > ...
> > + wait_event(pps->usage_queue, atomic_read(&pps->usage) == 0);
> > +
> > + pps_sysfs_remove_source_entry(pps);
> > + pps_unregister_cdev(pps);
> > + kfree(pps);
>
> This reference counting looks dubious to me... later on in the code
> you have:
>
> > +static int pps_cdev_open(struct inode *inode, struct file *file)
> > +{
> > + struct pps_device *pps = container_of(inode->i_cdev,
> > + struct pps_device, cdev);
> > +
> > + /* Lock the PPS source against (possible) deregistration */
> > + atomic_inc(&pps->usage);
>
> with no locking, so I see no reason why the atomic_inc() couldn't
> happen right after the wait_event() sees a count of 0 and lets the
> deregistration continue. Which would lead to use-after-free.
Mmm... you are right... can you please suggest to me how can I easily
fix this problem?
Ciao,
Rodolfo
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