From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH v3 for-next 01/13] IB/core: Use SRCU when reading client_list or device_list Date: Tue, 12 May 2015 12:23:32 -0600 Message-ID: <20150512182332.GD15891@obsidianresearch.com> References: <1431253604-9214-1-git-send-email-haggaie@mellanox.com> <1431253604-9214-2-git-send-email-haggaie@mellanox.com> <20150511181824.GA25405@obsidianresearch.com> <555198B7.40302@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <555198B7.40302@mellanox.com> Sender: netdev-owner@vger.kernel.org To: Haggai Eran Cc: Doug Ledford , linux-rdma@vger.kernel.org, netdev@vger.kernel.org, Liran Liss , Guy Shapiro , Shachar Raindel , Yotam Kenneth , Matan Barak List-Id: linux-rdma@vger.kernel.org On Tue, May 12, 2015 at 09:07:51AM +0300, Haggai Eran wrote: > > I'm not sure RCU is the right way to approach this. The driver core > > has the same basic task to perform, maybe review it's locking > > arrangment between the device list and driver list. > > > > [Actually we probably should be using the driver core here, with IB > > clients as device drivers, but that is way beyond scope of this..] > > So, I'm not very familiar with that code, but it seems that the main > difference is that in the core a single driver can be attached to a > device. Roughly, a bus (IB would be a bus) has devices attached to it, and devices have drivers attached to them. Bus:Device is 1:N, Device:Drvier is 1:1. There a a couple of reasons to be interested in re-using the driver core, perhaps the best is that it has all the infrastructure to let us auto-load client modules... > I guess a similar thing we can do is to rely on the context we associate > with a pair of a client and a device. If such a context exist, we don't > need to call client->add again. What do you think? I didn't look closely, isn't this enough? device_register: mutex_lock(client_mutex); down_write(devices_rwsem); list_add(device_list,dev,..); up_write(devices_rwsem); /* Caller must prevent device_register/unregister concurrancy on the same dev */ foreach(client_list) .. client->add(dev,...) .. mutex_unlock(client_mutex) client_register: mutex_lock(client_mutex) list_add(client_list,new_client..) down_read(devices_rwsem); foreach(device_list) .. client->add(dev,new_client,..) .. up_read(devices_rwsem); mutex_unlock(client_mutex) [Note, I didn't check this carefully, just intuitively seems like a sane starting point] Jason