Re: [PATCH net-next 1/7] r8152: adjust rx_bottom

[David Miller <davem@davemloft.net>]

From: Hayes Wang <hayeswang@realtek.com>
Date: Tue, 20 Jan 2015 02:48:50 +0000

>> >> +                       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.

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.