linux-kernel - Re: [RFC][PATCH -mm take5 4/7] using symlink for the net

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Date:	Wed, 13 Jun 2007 22:19:39 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Keiichi KII" <k-keiichi@...jp.nec.com>
Cc:	"Matt Mackall" <mpm@...enic.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"David Miller" <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [RFC][PATCH -mm take5 4/7] using symlink for the net_device

Hi,

On 6/13/07, Keiichi KII <k-keiichi@...jp.nec.com> wrote:
> [...]
> +static DECLARE_MUTEX(netdev_change_sem);

The preferred style these days is to use a DEFINE_MUTEX
(and the struct mutex primitives) for such locks that are used
as binary semaphores.

BTW, a comment here to note what this lock protects is required.
[ You don't really need to give a comment for the target_list_lock
because it's defined just below the "target_list". It's not equally obvious
at first glance what is protected by the netdev_change_sem, however. ]

> +       down(&netdev_change_sem);
> +       up(&netdev_change_sem);

So these become mutex_lock and mutex_unlock.

> +static int netconsole_event(struct notifier_block *this, unsigned long event,
> +                           void *ptr)
> +{
> +       int error = 0;
> +       unsigned long flags;
> +       char *old_link_name = NULL, *new_link_name = NULL;
> +       struct netconsole_target *nt, *tmp;
> +       struct net_device *dev = ptr;
> +       LIST_HEAD(modify_target_list);
> +
> +       if (event == NETDEV_CHANGENAME) {
> +               spin_lock_irqsave(&target_list_lock, flags);
> +               list_for_each_entry_safe(nt, tmp, &target_list, list)
> +                       if (nt->np.dev == dev)
> +                               list_move(&nt->list, &modify_target_list);
> +               spin_unlock_irqrestore(&target_list_lock, flags);
> +
> +               down(&netdev_change_sem);
> +               list_for_each_entry(nt, &modify_target_list, list) {
> +                       new_link_name = make_netdev_class_name(dev->name);
> +                       old_link_name = make_netdev_class_name(nt->np.dev_name);
> +                       if (!new_link_name || !old_link_name) {
> +                               printk(KERN_ERR "netconsole: "
> +                                      "make_netdev_class_name() failed!\n");
> +                               kfree(new_link_name);
> +                               kfree(old_link_name);
> +                               continue;

Sorry, but we're not covering from the error condition fully here. Note
that later you merge the temporary modify_target_list entirely back
into the target_list ... which would still contain these erroneous
nodes. A full cleanup (kobject_unregister the entry, and then list_del
from modify_target_list) is required here, before continuing.

> +                       }
> +                       sysfs_remove_link(&nt->obj, old_link_name);
> +                       error = sysfs_create_link(&nt->obj,
> +                                                 &nt->np.dev->dev.kobj,
> +                                                 new_link_name);
> +                       if (error)
> +                               printk(KERN_ERR "can't create link: %s\n",
> +                                      new_link_name);

Same here, a fuller cleanup is required to recover from the error
condition here, then kfree()'s and then stick a "continue;" here, else ...

> +                       strcpy(nt->np.dev_name, dev->name);

... you'll have move this up.

> +                       kfree(new_link_name);
> +                       kfree(old_link_name);
> +               }
> +               up(&netdev_change_sem);
> +
> +               spin_lock_irqsave(&target_list_lock, flags);
> +               list_for_each_entry_safe(nt, tmp, &modify_target_list, list)
> +                       list_move(&nt->list, &target_list);
> +               spin_unlock_irqrestore(&target_list_lock, flags);
> +       }
> +
> +       return NOTIFY_DONE;
> +}

Satyam
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