On 2024-05-07 at 12:33:39, Duoming Zhou ([email protected]) wrote:
> The origin ax25_dev_list implements its own single linked list,
> which is complicated and error-prone. For example, when deleting
> the node of ax25_dev_list in ax25_dev_device_down(), we have to
> operate on the head node and other nodes separately.
>
> This patch uses kernel universal linked list to replace original
> ax25_dev_list, which make the operation of ax25_dev_list easier.
> There are two points that need to notice:
>
> [1] We should add a check to judge whether the list is empty before
> INIT_LIST_HEAD in ax25_dev_device_up(), otherwise it will empty the
> list for each new ax25_dev added.
>
> [2] We should do "dev->ax25_ptr = ax25_dev;" and "dev->ax25_ptr = NULL;"
> while holding the spinlock, otherwise the ax25_dev_device_up() and
> ax25_dev_device_down() could race, we're not guaranteed to find a match
> ax25_dev in ax25_dev_device_down().
>
> Suggested-by: Dan Carpenter <[email protected]>
> Signed-off-by: Duoming Zhou <[email protected]>
> -ax25_dev *ax25_dev_list;
> +static struct list_head ax25_dev_list;
> DEFINE_SPINLOCK(ax25_dev_lock);
>
> ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
> @@ -34,7 +35,7 @@ ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
> ax25_dev *ax25_dev, *res = NULL;
>
> spin_lock_bh(&ax25_dev_lock);
> - for (ax25_dev = ax25_dev_list; ax25_dev != NULL; ax25_dev = ax25_dev->next)
> + list_for_each_entry(ax25_dev, &ax25_dev_list, list)
> if (ax25cmp(addr, (const ax25_address *)ax25_dev->dev->dev_addr) == 0) {
> res = ax25_dev;
> ax25_dev_hold(ax25_dev);
> @@ -52,6 +53,9 @@ void ax25_dev_device_up(struct net_device *dev)
> {
> ax25_dev *ax25_dev;
>
> + /* Initialized the list for the first entry */
> + if (!ax25_dev_list.next)
> + INIT_LIST_HEAD(&ax25_dev_list);
if you define ax25_dev_list using 'static LIST_HEAD(ax25_dev_list)', you need this conditional check and
initialization ?
> ax25_dev = kzalloc(sizeof(*ax25_dev), GFP_KERNEL);
> if (!ax25_dev) {
> printk(KERN_ERR "AX.25: ax25_dev_device_up - out of memory\n");
> @@ -59,7 +63,6 @@ void ax25_dev_device_up(struct net_device *dev)
> }
>
> refcount_set(&ax25_dev->refcount, 1);
>
On Tue, May 07, 2024 at 02:59:17PM +0530, Ratheesh Kannoth wrote:
> On 2024-05-07 at 12:33:39, Duoming Zhou ([email protected]) wrote:
> > The origin ax25_dev_list implements its own single linked list,
> > which is complicated and error-prone. For example, when deleting
> > the node of ax25_dev_list in ax25_dev_device_down(), we have to
> > operate on the head node and other nodes separately.
> >
> > This patch uses kernel universal linked list to replace original
> > ax25_dev_list, which make the operation of ax25_dev_list easier.
> > There are two points that need to notice:
> >
> > [1] We should add a check to judge whether the list is empty before
> > INIT_LIST_HEAD in ax25_dev_device_up(), otherwise it will empty the
> > list for each new ax25_dev added.
> >
> > [2] We should do "dev->ax25_ptr = ax25_dev;" and "dev->ax25_ptr = NULL;"
> > while holding the spinlock, otherwise the ax25_dev_device_up() and
> > ax25_dev_device_down() could race, we're not guaranteed to find a match
> > ax25_dev in ax25_dev_device_down().
> >
> > Suggested-by: Dan Carpenter <[email protected]>
> > Signed-off-by: Duoming Zhou <[email protected]>
> > -ax25_dev *ax25_dev_list;
> > +static struct list_head ax25_dev_list;
> > DEFINE_SPINLOCK(ax25_dev_lock);
> >
> > ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
> > @@ -34,7 +35,7 @@ ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
> > ax25_dev *ax25_dev, *res = NULL;
> >
> > spin_lock_bh(&ax25_dev_lock);
> > - for (ax25_dev = ax25_dev_list; ax25_dev != NULL; ax25_dev = ax25_dev->next)
> > + list_for_each_entry(ax25_dev, &ax25_dev_list, list)
> > if (ax25cmp(addr, (const ax25_address *)ax25_dev->dev->dev_addr) == 0) {
> > res = ax25_dev;
> > ax25_dev_hold(ax25_dev);
> > @@ -52,6 +53,9 @@ void ax25_dev_device_up(struct net_device *dev)
> > {
> > ax25_dev *ax25_dev;
> >
> > + /* Initialized the list for the first entry */
> > + if (!ax25_dev_list.next)
> > + INIT_LIST_HEAD(&ax25_dev_list);
> if you define ax25_dev_list using 'static LIST_HEAD(ax25_dev_list)', you need this conditional check and
> initialization ?
>
Ah, yes. That's the proper way to do it.
regards,
dan carpenter