linux-kernel - Re: [PATCH net-next 1/7] r8152: adjust rx

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Date:	Mon, 19 Jan 2015 21:52:20 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	hayeswang@...ltek.com
Cc:	sfeldma@...il.com, netdev@...r.kernel.org, nic_swsd@...ltek.com,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH net-next 1/7] r8152: adjust rx_bottom

From: Hayes Wang <hayeswang@...ltek.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.

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