linux-kernel - Re: [PATCH net v5 1/4] ax25: Use kernel universal linked list to implement ax25_dev

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Date: Tue, 7 May 2024 12:52:03 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Ratheesh Kannoth <rkannoth@...vell.com>
Cc: Duoming Zhou <duoming@....edu.cn>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hams@...r.kernel.org,
	pabeni@...hat.com, kuba@...nel.org, edumazet@...gle.com,
	jreuter@...na.de
Subject: Re: [PATCH net v5 1/4] ax25: Use kernel universal linked list to
 implement ax25_dev_list

On Tue, May 07, 2024 at 02:59:17PM +0530, Ratheesh Kannoth wrote:
> On 2024-05-07 at 12:33:39, Duoming Zhou (duoming@....edu.cn) 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 <dan.carpenter@...aro.org>
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > -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