netdev - RE: [PATCH net-next 1/7] r8152: adjust rx

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Date:	Tue, 20 Jan 2015 02:48:50 +0000
From:	Hayes Wang <hayeswang@...ltek.com>
To:	David Miller <davem@...emloft.net>,
	"sfeldma@...il.com" <sfeldma@...il.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	nic_swsd <nic_swsd@...ltek.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: RE: [PATCH net-next 1/7] r8152: adjust rx_bottom

 David Miller [mailto:davem@...emloft.net] 
> Sent: Tuesday, January 20, 2015 5:14 AM
[...]
> >> -               r8152_submit_rx(tp, agg, GFP_ATOMIC);
> >> +               if (!ret) {
> >> +                       ret = r8152_submit_rx(tp, agg, GFP_ATOMIC);
> >> +               } else {
> >> +                       urb->actual_length = 0;
> >> +                       list_add_tail(&agg->list, next);
> > 
> > Do you need a spin_lock_irqsave(&tp->rx_lock, flags) around this?
> 
> Indeed, and rtl_start_rx() seems to also access agg->list without
> proper locking.

It is unnecessary because I deal with them in a local list_head. My steps are
   1. Move the whole list from tp->rx_done to local rx_queue. (with spin lock)
   2. dequeue/enqueue the lists in rx_queue.
   3. Move the lists in rx_queue to tp->rx_done if it is necessary. (spin lock)
For step 2, it wouldn't have race, because the list_head is local and no other
function would change it. Therefore, I don't think it needs the spin lock.

The rtl_start_rx() also uses the similar way.
 
Best Regards,
Hayes
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