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

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Date:	Tue, 20 Jan 2015 03:24:52 +0000
From:	Hayes Wang <hayeswang@...ltek.com>
To:	David Miller <davem@...emloft.net>
CC:	"sfeldma@...il.com" <sfeldma@...il.com>,
	"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 10:52 AM
[...]
> agg->list is not local, you have to use a spinlock to protect
> modifications to it, some other sites which modify agg->list do take
> the lock properly.
> 
> You cannot modify a list like agg->list without proper locking.

Excuse me. I don't understand.

Before step1
   tp_rx_done->listA->listB->listC->listD->...
   rx_queue->
Because the other function would chage tp->rx_done,
I need move the lists with spin lock.

After step1
   tp_rx_done->
   rx_queue->listA->listB->listC->listD->...

Now I dequeue one of the lists from the list_head and
deal with it.
   tp_rx_done->
   rx_queue->listA->listC->listD->...
                    listB

Then, if I want to put it back to rx_queue, I have to
use spin lock. Why? No other function would chage
rx_queue and the items in it.
 
Best Regards,
Hayes
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