From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next 1/7] r8152: adjust rx_bottom Date: Mon, 19 Jan 2015 21:52:20 -0500 (EST) Message-ID: <20150119.215220.720365670558757349.davem@davemloft.net> References: <20150119.161333.1471925264489559119.davem@davemloft.net> <0835B3720019904CB8F7AA43166CEEB2EE6E76@RTITMBSV03.realtek.com.tw> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: sfeldma@gmail.com, netdev@vger.kernel.org, nic_swsd@realtek.com, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org To: hayeswang@realtek.com Return-path: In-Reply-To: <0835B3720019904CB8F7AA43166CEEB2EE6E76@RTITMBSV03.realtek.com.tw> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Hayes Wang 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.